How do i solve this

Question

A 500-gallon backyard swimming pool that contains 300 gallons of water is being drained through a hose. During the first 3 hours, the pool drains at a rate of 40 gallons per hour. During the next 9 hours the pool drains at a rate of 20 gallons per hour. Which of the following functions represents the volume of water in the pool at time t, where 0 <= t <= 12 ?

Answer 1

300-40t ... 0<t<3

180 -20(t-3) ... 3<t<12

Answer 2

This is algebra, not Differential equations: The rates are constant and subtract from the volume proportional to the time.

From 0 to 3 hours: V = 300 - 40t

After 3 hours, the new volume is 300 - 120 = 180 and if you want to use the original t, you need for the function to start emptying at t = 3 seconds:

from 3 to 9 hours V = 180 - 20(t-3)