The full tank has a volume of x litres.
The tank is 1/6 full, so it has (1/6)x litres of gasoline.
Now you add 8 litres. The tank now has (1/6)x + 8 litres.
It is now 1/4 full. 1/4 full means it has (1/4)x litres.
Therefore, (1/6)x + 8 must equal (1/4)x.
(1/6)x + 8 = (1/4)x
Multiply both sides by the LCD which is 12.
12(1/6)x + 12(8) = 12(1/4)x
2x + 96 = 3x
Subtract 2x from both sides.
96 = x
x = 96
Answer: The tank holds 96 litres.