Answer:
I think that there might be some complex differential equation
stuff going on here if this were in the real world, but for the sake of this problem... may I suggest that the tank is filling up at a rate of
1/8 of a tank per hour...
it is evaporating at a rate of 1/12 tank per hour
you can subtract the rates
1/8 - 1/12 = 12/96- 8/96 = 3/96 = 1/32 tank/hr
so to fill the tank it should take 32 hours...
I think the logic and math work... lets see if someone else will verify this analysis?
Explanation: