An oil tanker is leaking at a constant rate per minute. After 12 minutes, 537 gallons of oil remain in the tanker. After 16 minutes, 336 gallons of oil remain in the tanker. Write the function f(t) that describes this scenario.
You need to find the rate of change and the initial value of the function and write it in f(t) = mt + b form, where 'm' is the rate of change and 'b' is the initial value.