Find the curved surface area of the frustrum in the figure

Correct Answer: Option B

Explanation

(frac{x}{4} = frac{6 + x}{6})
6x = 4(6 + x) = 24 + 4x
x = 12cm 

 CSA = (pi RL – pi rl)
= (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