You are standing on the bank of a river that is 1 mile wide and want to get to a town on the opposite bank, 1 mile upstream. You plan to row on a straight line to some point R on the opposite bank and...

You are standing on the bank of a river that is 1 mile wide and want to get to a town on the
opposite bank, 1 mile upstream. You plan to row on a straight line to some point R on the
opposite bank and then walk the remaining distance along the bank. To what point R should you
row to reach the town in the shortest possible time, if you can row at 4 miles/hr and walk at 5
miles/ hr?