Answer: 834 days
Explanation:
The tank will be half full when it has lost 100 L.
Convert that to milliliters so that it can be compared with the loss rate:
1 l = 1,000 ml
100 l = 100 * 1,000
= 100,000 ml
The rate of loss is 120 ml per day. To lose 100,000 ml, the leak would have to have been going on for:
= 100,000 / 120
= 833.3
= 834 days (less than half full)