Answer:
2.375 gallons left
(This answer is valid if the question allows for your answer to be in decimals rather than as a fraction)
Explanation:
Calculate 1/8 = 0.125
1 1/8 is 1 + 0.125 = 1.125
Calculate 1/2 = 0.5
3 1/2 is 3 + 0.5 = 3.5
3.5 - 1.125 = 2.375