Speed of Boat that you are taking to the Island =x Km/hr or x m/sec.
Let u Km/hr or x m/sec, be the speed of water.
⇒Speed of Water while Going Upstream
=Speed of Boat+Speed of Water
=(x+u) Km/hr or (x-u) m/sec.
⇒Speed of Water while Going Downstream, that is speed of the boat coming back from the island
=Speed of Boat-Speed of Water
=(x-u) Km/hr or (x-u) m/sec.
