1. the level of a leaking oil-storage tank drops by 0.1% of the height above a leak every hour. The leak(hole) starts at a height of 4.5m above the ground at 2 am. The tank is a large cylinder of diameter 20m and total height 10m, but is only three-quarters full when it starts leaking.
A spillage of more than 5000L must be notified to the environment protection Agency. By what time should the leak be fixed to avoid notification?
(I don't know how to set up the formula of oil decreasing)