A man can swim in still water at a speed of 5kmph. He desires to cross a river flowing at a speed of 4 kmph in the shortest time interval. The direction in which he has to swim is

making an angle ${\tan }^{–1}3/4$ with the normal to the river flow

making an angle ${\cos }^{–1}3/4$ with the normal to the river flow

making an angle ${\sin }^{–1}3/4$ with the normal to the river flow

making an angle ${90}^0$ with the river flow