A swimmer swims north at 0.15 m/s relative to still water across a river that flows at

Question:

A swimmer swims north at 0.15 m/s relative to still water across a river that flows at a rate of 0.20 m/s from west to east.
(a) The general direction of the swimmer’s velocity, relative to the riverbank, is (1) north of east, (2) south of west, (3) north of west, (4) south of east.
(b) Calculate the swimmer’s velocity relative to the riverbank.