Answer: 51 liters of fuel is needed more to fill the tank
Step-by-step explanation:
When the gauge is full, the volume of fuel in the tank is 68 liters.
Now it is 1/4 full.
The amount of fuel it has when it is 1/4 full would be 1/4 * 68 = 17 liters
Now, we need to know how many more liters of fuel until the tank is full.
What we just need to do here is to subtract the volume when it is quarter full from the volume when it is full.
That would be 68 liters - 17 liters = 51 liters