-15x + 210 = 90 (I got 210 because it’s the distance the line is on now)
So -15x = 90 - 210
-15x = -120
Divide both sides by -15 that equals 8 so the your answer is but if it’s the time before the draining began (I will assume at 0) then the answer would be 3 + 8, it will be 11 hours for it to reach 90
