Answer:
17/8 gallons
Explanation:
18/6 gallons in the tank.
Before that, she fill 7/8 gallons.
So,
18/6 - 7/8
Subtracting both of these are impossible since the denominators are not equal.
We can do this by multiplying each other's numerator and denominator by their other denominator.
6 × 8 = 48
18 × 8 = 144
8 × 6 = 48
7 × 6 = 42
144 / 48 - 42 / 48
We can now subtract this. Note: do not subtract the denominator.
144 - 42 = 102
102 / 48
17/8
So,
There is 17/8 of gallons in the tank before filling it.