A swimming pool with a rectangular surface 18m long and 12m wide, is being filled at the rate of 0.8m^3/min. At one end, it is 1m deep, and at the other end, it is 2.5m deep with a constant slope in between. How fast is the water rising when the depth of the water at the deep end is 1m?

The answer is .0056m/min. I haven't the slightest clue how to get that.