I would appreciate help with this question, thanks.

A triangular window, with its top edge horizontal, is built in the side of a water tank. The window is 18 m tall, 9 m wide at the top, and can hold back 40 kN of force. Water is added to the tank until the window is about to burst. If the density of water is 1000 kg/m and we approximate the gravitational constant as 10 m/s, how high is the water above the bottom corner