With your problem you have r = 10, h = 10. That means the maximum volume is:
The actual volume is three quarter of the maxium volume:
that means the surface of the oil is 7.5 m above ground. So the height above the leak is 3 m:
2. Calculate the volume which has already leaked from the tank:
Since 5000 L = 5 m³ you have to solve for t:
Use logarithms to calculate t. I've got t ≈ 0.0505 h and that are nearly 3 min (This result seems a little funny to me
I assume that I've made a silly mistake with my calculations. So check!