The amount of water in a bathtube as it drains can be modeled by this equation with y representing the number of gallons of water in the tub and x representing the time, in minutes, that the tube has been draining y=-7.3x+39.7 after how many minutes will the tub have 17.8 gallons of water remaining

Since  is representing the number of gallons of water in the tub, we need to replace  with the number of gallons remaining in the tube to find the time. Fortunately, the problem is telling us  just that: 17.8 gallons. The only thing left is replacing that value in the equation, and solve for  to find the time:





We can conclude that after 3 minutes the tub will have 17.8 gallons of water remaining.