Water depth in a triangular trough holding 15 gallons

[JudasIscariot]

Beginner in Physics... Please Help!

A trough is formed by nailing together edge to edge, two boards 11 ft. in length, so that the right section is a right triangle. If 15 gal of water are poured into the trough and if the trough is held level so that a right section of the water is an isosceles right triangle, how deep is the water?! (231 cu in. = 1 gal)

 

[Fredrik]

You should probably post this in the homework help forum, and also show us what you've done so far. (Read the sticky post at the top of that forum).