Calculating Water Level Rise in Trapezoid Trough

[rocomath]

Homework Statement

A water trough is 10m long and a cross-section has a shape of an isosceles trapezoid that is 30cm wide at the bottom, 80cm wide at the top, and has a height of 50cm. If the bottom of the trough is being filled with water at the rate of .2m^3/min, how fast is the water level rising when the water is 30cm deep?

Homework Equations

A (trapezoid) = .5(b1+b2)

The Attempt at a Solution

http://img218.imageshack.us/img218/5321/22806877ce9.jpg

 

[rocomath]

nvm i got it, my geometry isn't that great but i pulled through!