a tank is 1/6 full of gasoline. If 8 litres are added it would be 1/4 full. how many litres does the tank hold?

Find a common denominator between the two

1/6 - 2/12

1/4 - 3/12

3/12 - 2/12 because 2/12 is what you started with

= 1/12

If 1/12 is 8 litres, it's 8 x 12 = 96

The tank can hold 96 litres.