Answer:Stan used 19/40 of a gallon of gasoline.
Step-by-step explanation:
At first, Stan's lawn mower had 1/8 of a gallon of gasoline in the tank. When it got finished, he put 6/10 of a gallon of gasoline in the tank. It means that the number of gallons of gasoline that he has already put in the tank is
1/8 + 6/10 = 29/40 of a gallon.
After he mowed, 1/4 of a gallon was left in the tank. Therefore, the total amount of gasoline Stan used is
29/40 - 1/4 = 19/40 of a gallon