Calculate the area of the trapezium with parallel sides 7 cm and 21 cm, and a height of 14 cm.

Step 1: Calculate the area of the trapezium (Question 18).
The formula for the area of a trapezium is given by:

$$\text{Area} = \frac{1}{2}(a+b)h$$

where $a$ and $b$ are the lengths of the parallel sides, and $h$ is the perpendicular height.
From the image, we have:
$a = 7 \text{ cm}$
$b = 21 \text{ cm}$
$h = 14 \text{ cm}$

Substitute these values into the formula:

$$\text{Area} = \frac{1}{2}(7 \text{ cm} + 21 \text{ cm})(14 \text{ cm})$$ $$\text{Area} = \frac{1}{2}(28 \text{ cm})(14 \text{ cm})$$ $$\text{Area} = (14 \text{ cm})(14 \text{ cm})$$ $$\text{Area} = \boxed{\text{196 cm}^2}$$