La respuesta es 5a - 8b + 4
Sonia saves a lot of water. To figure this out, you plug the number 8 into the equation, replacing it with the variable x. y = 3(8). Therefore, y=24. To find out how much water she saves, you have to also figure out how much water she was using for 8 minutes with the other shower head, the one that wastes the water. Since it dispenses 12 gallons per minute, you multiply that by 8 minutes and get 96. Subtract 24 from 96 and get 72. Which I think is your answer. Then again, I'm in high school so I most likely am wrong.
This will help a lot if you go to desmos! Just graph the equation on there! It’s much easier to see on computer