Answer: 48 gallons
Explanation:
Given: Previous rate of dispensing water= 9 gallons per min
If Reyna use 8 min showerhead then
Total amount of water dispensed=

After Reyna changed the showerhead to energy saving with equation
y=3x, where y is the amount of water dispensed as a function of the number of x minutes for the new showerhead.
When we put x=8 minutes, we get total amount of water dispensed=

Water saved by Reyna=72-24=48 gallons