# Thread: Calculating depth of water

1. ## Calculating depth of water

I know a) is 81cm^3 but Im stuck on b

2. ## Re: Calculating depth of water

You wind up with a trianglular prism. Its volume is 81. The volume of the prism is the area of the end triangle times the length. you know the length is 9. The area of a triangle is $\dfrac{1}{2}bh$. You know the triangle is a 45-45-90 triangle. If you draw in the height, you know that you are cutting the 90 degree angle in half, so you get another 45-45-90 triangle with the height and half the base as equal sides in the isosceles triangle. So, you have:

$\dfrac{1}{2}bh\cdot 9 = 81$

and

$h = \dfrac{1}{2}b$

Can you solve it from here?

h=3