The amount of water in a bathtub 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 tub has been draining. y=−7.3x+39.7 After how many minutes will the tub have 17.8 gallons of water remaining? Enter your answer in the box.

y = -7.3x + 39.7
 The first thing we must do for this case is to make use of the given equation and replace the value of y:
 17.8 = -7.3x + 39.7
 Now we clear x:
 7.3x = 39.7-17.8
 x = (39.7-17.8) / (7.3)
 x = 3
 Answer:
 the tub will have 17.8 gallons of water remaining after 3 minutes