Question on: JAMB Mathematics - 1990

(\frac{x}{4} = \frac{6 + x}{6})

6x = 4(6 + x) = 24 + 4x

x = 12 = c = (\pi RL - \pi L)

= (\pi (6) \sqrt{18^2} + 6^2 - \pi \times 4 \times \sqrt{12^2} + 4^2)

= 6(\pi \sqrt{360} - 4 \pi \sqrt{160})

= 36(\pi \sqrt{10} - 16 \pi \sqrt{10})

= 20(\pi \sqrt{10})cm²