A tub of water is emptied at a rate of 3 gallons per minute. The equation y –12 = –3(x – 1) models the amount of water remaining, where x is time (in minutes) and y is the amount of water left (in gallons). Analyze the work shown below to determine the initial amount of water.

1. Solve for the y-variable.

y – 12 = –3(x – 1)

y – 12 = –3x + 3

y = –3x +15

2. Write the equation using function notation.

f(x) = –3x +15

The tub started with
gallons of water.