Sheila had 1 gallon of milk. she used 1/4 of a gallon of milk and she used 1/6 of a gallon of milk. how much milk is left

We know that
1) Sheila had 1 gallon of milk
2) she used 1/4 of a gallon of milk > 1-1/4> 3/4 gallon left
3) she used 1/6 of a gallon of milk> 3/4-1/6---> (6*3-4*1)/24---> 14/24
14/24> 7/12 gallon

the answer is
7/12 gallon