Problem 425. ranch area?

Your friend has a ranch with four distinct boundary lines. Three boundary lines are ideal straight roads: (1) North Club Road, (2) East Cathedral Road, and (3) North Market Road. The fourth boundary line is the Threadwater Canal. The length of the second boundary line is exactly one mile. You have visualized that any point on the Threadwater Canal is defined by cartesian coordinates x and y in miles, where x is its distance from North Club Road, and y is its distance from East Cathedral Road. A surveyor has found the function y(x) for you. She also told you that one square mile is 640 acres. She wants you to calculate the area of this ranch in acres.