Which is greater: a) 2/7 of 3/4 or 3/5 of 5/8? b) 1/2 of 6/7 or 2/3 of 3/7?

To compare, find a common denominator, which is 56. $\frac{3}{14} = \frac{3 \times 4}{14 \times 4} = \frac{12}{56}$ $\frac{3}{8} = \frac{3 \times 7}{8 \times 7} = \frac{21}{56}$ Since $\frac{21}{56} > \frac{12}{56}$, then $\frac{3}{8}$ is greater.
Therefore, $\frac{3}{5}$ of $\frac{5}{8}$ is greater. $\boxed{\frac{3}{5} \text{ of } \frac{5}{8}}$

• b) $\frac{1}{2}$ of $\frac{6}{7}$ or $\frac{2}{3}$ of $\frac{3}{7}$

Since the denominators are the same, compare the numerators. $3 > 2$.  
Therefore, $\frac{3}{7}$ is greater.
$$
\boxed{\frac{1}{2} \text{ of } \frac{6}{7}}
$$

5. Saili plants 4 saplings, in a row, in her garden. The distance between two adjacent saplings is $\frac{3}{4}$ m. Find the distance between the first and the last sapling.

For 4 saplings planted in a row, there are $4 - 1 = 3$ gaps.

The distance between the first and the last sapling is the number of gaps multiplied by the distance between adjacent saplings.

The distance between the first and the last sapling is $\boxed{2\frac{1}{4} \text{ m}}$.

6. Lipika reads a book for $1\frac{3}{4}$ hours everyday. She reads the entire book in 6 days. How many hours in all were required by her to read the book?

Total hours = (Hours read per day) $\times$ (Number of days)

Lipika required $\boxed{10\frac{1}{2} \text{ hours}}$ to read the book.

7. A car runs 16 km using 1 litre of petrol. How much distance will it cover using $2\frac{3}{4}$ litres of petrol.

Distance covered = (Distance per litre) $\times$ (Total litres of petrol)

The car will cover $\boxed{44 \text{ km}}$.