Trough

Problem 13
A trapezoidal trough is 10 ft long, 4 ft wide at the top, 2 ft wide at the bottom and 2 ft deep. If water flows in at 10 ft³/min, find how fast the surface is rising, when the water is 6 in deep.

Problem 04
A triangular trough 10 ft long is 4 ft across the top, and 4 ft deep. If water flows in at the rate of 3 ft³/min, find how fast the surface is rising when the water is 6 in deep.

Problem 03
A rectangular trough is 10 ft long and 3 ft wide. Find how fast the surface rises, if water flows in at the rate of 12 ft³/min.