a generator needs a fixed amount of fuel to keep it running two hours a day. After running for 6 days, the generators fuel tank was 2/3 full. After 11 more days, 3 1/2 liters of fuel was left in the tank. If the tank was originally full, how much fuel can the tank hold?

63 liters

Explanation:

The amount of fuel used per day is ...

... (1 tank - 2/3 tank) / (6 days) = (1/3 tank) / (6 days) = (1/18) tank/day

Then the amount of fuel used after 6+11 = 17 days is

... (17 days) * (1/18 tank/day) = 17/18 tank

and the amount remaining is ...

... (1 tank - 17/18 tank) = 1/18 tank = 3 1/2 liters

To find the tank size, we can multiply this result by 18:

... 1 tank = 18 * (3 1/2 liters) = 63 liters