Atrough is 12 ft long and its ends have the shape of isosceles triangles that are 5 ft across at the top and have a height of 1 ft. if the trough is being filled with water at a rate of 13 ft3/min, how fast is the water level rising when the water is 8 inches deep? i have been getting 13/30, but apparently, that is wrong? v=.5 * h * l * b because of similar triangles: b = 5h (b/h = 5/1) l = 12 v = .5 * h * 5h * 12 v = 30h^2 (dv/dt) = 60 h (dh/dt) dv/dt = 13 h = .5 (because this is in feet) 13 = 60*.5(dh/dt) 13/30 = dh/dt