A lawn shaped like a trapezium has parallel sides 18 m and 12 m, with 9 m between them. Laying turf costs ₹45 per square metre. What is the total cost?

**Area of a trapezium = ½ × (sum of parallel sides) × height.**

The height is the **perpendicular distance** between the two parallel sides — NOT the slant length of the non-parallel side.

Example: parallel sides 8 cm and 5 cm, height 4 cm. Area = ½ × $(8+5)\times 4$ = ½ × $13\times 4=26{\text{cm}}^2$.

Why ½? You can split a trapezium into a rectangle plus a triangle (or chop and rearrange into a rectangle of the average parallel side). The factor of ½ comes from averaging the two parallel sides.