Once they're empty, I guess.
Did you put it the wrong way around?
Because it would be after four hours in this case.
Answer:
7.5
Step-by-step explanation:
CUZZ IM HOTTTTTTTTTTTTTTTT'
To find p, you would first subtract the 4 from either side of the equation. You would then have 3p+15. Then you would divide by 3 on both sides to get 9=5.
Therefore, p=5