A river is flowing at a speed u. A swimmer can swim relative to the stream at speed v. * If the swimmer swims upstream a distance d and then return to their starting point, find the time t it takes in terms of d, v, and u. (5) * If the swimmer swims in a direction so that they cross directly across the stream relative to Earth (perpendicular to ), find the time t it takes in terms of d, v, and u