25% ඞෟ෽෮෪ ෤෡෮෤෠෮෣෮ ෣෣ ෤෡෮෣෮.

Step 1: Convert the percentage to a fraction by dividing by 100. $25\% = \frac{25}{100}$ Step 2: Simplify the fraction. $\frac{25}{100} = \frac{1}{4}$ The final answer is $\boxed{\frac{1}{4}}$.

Step 1: Convert the whole number to a fraction with the same denominator. $3 = \frac{3 \times 5}{5} = \frac{15}{5}$ Step 2: Add the fractions. $\frac{3}{5} + \frac{15}{5} = \frac{3+15}{5} = \frac{18}{5}$ The final answer is $\boxed{\frac{18}{5}}$.

Step 1: Recognize the relationship between the given multiplication and the required multiplication. Given: $273 \times 31 = 8463$. We need to find $0.031 \times 2.73$. Notice that $0.031 = 31 \times 0.001$ and $2.73 = 273 \times 0.01$. Step 2: Rewrite the expression using the given numbers and decimal factors. $0.031 \times 2.73 = (31 \times 0.001) \times (273 \times 0.01)$ $0.031 \times 2.73 = (273 \times 31) \times (0.001 \times 0.01)$ Step 3: Substitute the given product and multiply the decimal factors. $0.031 \times 2.73 = 8463 \times 0.00001$ $0.031 \times 2.73 = 0.08463$ The final answer is $\boxed{0.08463}$.

i) Step 1: List all the unique letters in the word ANURADHAPURA. The unique letters are A, N, U, R, D, H, P. The elements of the set B are $\boxed{{A, N, U, R, D, H, P}}$.

ii) Step 1: Count the number of unique elements in the set B. There are 7 unique letters. So, n(B) = $\boxed{7}$.

Step 1: Add the time difference to the Sri Lankan time. Sri Lanka time: 9:15 AM on 2025-06-15 Time difference: +10 hours $9:15 AM + 10 hours = 19:15$ Step 2: Convert the 24-hour format time to 12-hour format. 19:15 is 7:15 PM. The date remains the same. The time in Sydney will be $\boxed{2025-06-15, 7:15 PM}$.

Step 1: Find the square root of 576. We know that $20^2 = 400$ and $30^2 = 900$. The number ends in 6, so its square root must end in 4 or 6. Let's test 24: $24 \times 24 = 576$ The final answer is $\boxed{24}$.

Step 1: Recall the conversion factor between tonnes (t) and kilograms (kg). $1 t = 1000 \text{ kg}$ Step 2: Multiply the given value in tonnes by the conversion factor. $7.875 t \times 1000 \frac{kg}{t} = 7875 \text{ kg}$ The final answer is $\boxed{7875 kg}$.

Step 1: Calculate the cube of -2. $(-2)^3 = (-2) \times (-2) \times (-2)$ Step 2: Perform the multiplication. $(-2) \times (-2) = 4$ $4 \times (-2) = -8$ The final answer is $\boxed{-8}$.

Step 1: Calculate the area of $\triangle ABC$ using the base BC and its corresponding height AE. $\text{Area} = \frac{1}{2} \times base \times \text{height}$ $\text{Area} = \frac{1}{2} \times BC \times AE$ $\text{Area} = \frac{1}{2} \times 12 cm \times 5 \text{ cm}$ $\text{Area} = 30 cm^2$ Step 2: Use the calculated area and the other given height CD to find the length of its corresponding base AB. $\text{Area} = \frac{1}{2} \times AB \times CD$ $30 cm^2 = \frac{1}{2} \times AB \times 6 \text{ cm}$ Step 3: Solve for AB. $30 = 3 \times AB$ $AB = \frac{30}{3}$ $AB = 10 \text{ cm}$ The final answer is $\boxed{10 cm}$.

Step 1: Identify the angles in the right-angled triangle. One angle is $90^\circ$ (right angle). One acute angle is $35^\circ$. The other acute angle is $x^\circ$. Step 2: Use the property that the sum of angles in a triangle is $180^\circ$. $x^\circ + 35^\circ + 90^\circ = 180^\circ$ Step 3: Solve for $x^\circ$. $x^\circ + 125^\circ = 180^\circ$ $x^\circ = 180^\circ - 125^\circ$ $x^\circ = 55^\circ$ The final answer is $\boxed{55^\circ}$.

Step 1: Let the monthly salary be $S$. According to the problem, 5% of the monthly salary is Rs. 4000. $5\% of S = 4000$ Step 2: Convert the percentage to a fraction and set up the equation. $\frac{5}{100} \times S = 4000$ Step 3: Solve for $S$. $S = 4000 \times \frac{100}{5}$ $S = 4000 \times 20$ $S = 80000$ Mr. Perera's monthly salary is $\boxed{Rs. 80000}$.