A man stands at a point A on the bank of a straight river, 1 mi wide. To reach point B, L = 4 mi downstream on the opposite bank, he first rows his boat to point P on the opposite bank and then walks the remaining distance x to B, as shown in the figure. He can row at a speed of 2 mi/h and walk at a speed of 5 mi/h. Find a function that models the time needed for the trip. And Where should he land so that he reaches B as soon as possible?