A swimmer can swim with `5ms^(-1)` in still water. He wants to cross a river having width 200m heading perpendicular to the flow. Speed of flow is uniformly increasing from zero at side to `3ms^(-1)` at mid from both side of the river. Then the time taken by the swimmer to cross the river will be
A. 40sec
B. 60sec
C. 80sec
D. 90sec
