Atub 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.