A cuboidal block of metal 9 cm × 6 cm × 4 cm is melted and recast into small cubes of side 3 cm. How many such cubes are obtained?

**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.