Engineers are draining a water reservoir until its depth is only 10 feet. The depth decreases exponentially as shown in the graph below. The engineers measure the depth after 1 hour to be 64 feet and after 4 hours to be 28 feet. Develop an exponential equation in y=a(b)^2 to predict the depth as a function of hours draining. Round a to the nearest integer and b to the nearest hundredth. The, graph the horizontal line y = 10 and find its intersection to determine the time, to the nearest tenth of an hour, when will the reservoir reach a depth of 10 feet?