Question

A boat moving upstream with velocity 3 w.r.t. ground. An observer standing on boat observes that swimmer 'S' is crossing the river perpendicular to the direction of motion of boat. If river velocity is 4m/s & swimmer crosses the river width 100 m in 50 sec then -

1. Velocity of swimmer w.r.t. ground is    
2. Velocity of swimmer w.r.t. ground is    
3. Drift of swimmer along river is zero    
4. Drift of swimmer along river will be 50 m