Answer:
Step-by-step explanation:
River is 7.5 m wide . Time taken by it cover this displacement
= displacement / velocity
= 7.5 / 0.4
= 18.75 s
During this period , swimmer will have a displacement of 30 m due to velocity of river water .
Displacement of 30 m downstream will be due to flow of river .
velocity of water flow = displacement / time
= 30 / 18.75
= 1.6 m /s