# Math Help - Area of a frustum

1. ## Area of a frustum

I know that $A=\pi (R+r)\sqrt{(R-r)^2+h^2}$

Question: Two mathematically similar frustums have heights of 20 and 30cm. The surface area of the smaller frustum is 450cm^2.

Calculate the surfce area of the larger frustum

My workings:
$450=(\pi R+r)^2\cdot (R-r)^2+400$

$50=(\pi (R+r))^2(R-r)^2$