Find the area of a trapezium whose parallel sides are 24 cm

Area of a trapezium $=\frac{1}{2} \times($ Sum of parallel sides $) \times($ Distance between them $)$

$=\left\{\frac{1}{2} \times(24+20) \times 15\right\} \mathrm{cm}^{2}$

$=\left(\frac{1}{2} \times 44 \times 15\right) \mathrm{cm}^{2}$

$=(22 \times 15) \mathrm{cm}^{2}$

$=330 \mathrm{~cm}^{2}$

Hence, the area of the trapezium is $330 \mathrm{~cm}^{2}$.