A tank is in the shape of 1m x 1m x 1m cube and is positioned with its base in a horizontal position.There is a amall hole in the side of the tank at a height of 80cm above the base.At 12.00 water starts to enter the empty tank , and the rate at which the water is entering t minutes later is given in litres per minute by the formula 20+2t.

At what time does the water start to exit the tank through the small hole?

I don't even know where to start!

please help!