To find the area of a trapezium, you need to use the formula: A = 1/2 × (a + b) × h, where a and b are the lengths of the parallel sides, and h is the distance between them.

In this case, a = 12 cm, b = 20 cm, and h = 15 cm.

So, substituting these values into the formula:

A = 1/2 × (12 + 20) × 15

A = 1/2 × 32 × 15

A = 240 cm²

Therefore, the area of the trapezium is 240 cm².