The diagram shows the cross-section, shown shaded, of a mathematical instrument. The length of the base of the instrument is 9 cm and the height is 15 cm. The base and the height of the instrument are at right angles.

1. aCalculate the area of the outer triangle. [2]
2. bThe base and height of the inner triangle are each 1/3 of the base and height of the outer triangle. Calculate the height of the inner triangle. [1]
3. cCalculate the area of the shaded part. [2]

You'll mark your own answer against the marking guide when you hand it in.