Answer:11.25
Step-by-step explanation:because we have to find out how many gallons we have in one hour so you divide both sides by 4
4/4 is 1 hour
3/4 is 0.75 gallons then you have to multiply both sides by 15
1 hour times 15 is 15 hours
the 0.75 x 15 is 11.25
so the answer is 11.25 gallons that she uses in 15 hours
hope this helps