The correct option is A 30 litres
Let quantity of water in tank B be x litres.
Then quantity of water in the tank A=5x litres
Total water in both the tanks =x+5x
=90 liters
⇒6x=90⇒x=15
∴ Water in tank B=15 litres
⇒ Water in tank A=15×5=75 litres
So, quantity of water to be transferred from tank A to tank B, so that each tank contains 45 litres=75−30=45 litres
Therefore, 30 liters of water should be transferred.