Good Questions for Calculus

Problem setting: A man with a boat at point S at sea wants to get to point Q inland. Point S is distance d1 from the closest point P on the shore, point Q is distance d2 from the closest point T on the shore and point P and T are at a distance of d.

Question: If the man rows with a speed of vr  and walks with a speed of vw  at what point R should he beach the boat in order to get from point S to point Q in the least possible time?