Problem 4: A semi carrying a tank of organic solvent wrecks and spills into a canal 12 miles upstream of a small lake. The canal is 5 feet wide, 4.2 fet deep and is flowing at a velocity of 0.35ft/s. The lake has an approximate water volume of 122 acre-ft. Assume that the lake behaves as a CSTR and the river like a PFR. Estimate how long it will take from the time of the spill to flush 99% of the solvent from the lake. Report your answer in days