Find a common denominator for the fractions.

The denominators are 5 and 7. The least common multiple of 5 and 7 is $5 \times 7 = 35$.

The fraction is in its simplest form as 81 and 35 have no common factors other than 1. It can also be expressed as a mixed number.

So, $\frac{81}{35} = 2\frac{11}{35}$.

The simplified expression is $\boxed{\frac{81}{35}}$ or $\boxed{2\frac{11}{35}}$.

4. b)

Given that 3 kg of meat costs Gh¢60.
Cost per kg = $\frac{\text{Total Cost}}{\text{Weight}} = \frac{60 \text{ Gh¢}}{3 \text{ kg}} = 20 \text{ Gh¢/kg}$.

For 2 kg: Cost = $2 \text{ kg} \times 20 \text{ Gh¢/kg} = 40 \text{ Gh¢}$.
For 5 kg: Cost = $5 \text{ kg} \times 20 \text{ Gh¢/kg} = 100 \text{ Gh¢}$.
For 12 kg: Cost = $12 \text{ kg} \times 20 \text{ Gh¢/kg} = 240 \text{ Gh¢}$.

4. c)

For $x = -2$:

For $x = -1$:

For $x = 0$:

For $x = 1$:

For $x = 2$:

5. a)

Length $L = 12.8$ m
Width $W = 7.5$ m

The perimeter of the rectangle is $\boxed{40.6 \text{ m}}$.

5. b)

Divide the numerical coefficients:

Divide the variable terms using the rule $x^m/x^n = x^{m-n}$:

Combine the simplified terms:

The simplified and evaluated expression is $\boxed{-\frac{1}{24}}$.

5. c)

The two angles given are $(3y + 5)^\circ$ and $(2y + 15)^\circ$.

The value of $y$ is $\boxed{32}$.