Answer
subtraction;
$8(7-2.5)=56-20$
$36$ gallons of water are saved.
Work Step by Step
To represent water saved each day, an expression involving subtracting should be used.
Using $a(b+c)=ab+ac$ or the Distributive Property, the amount of water saved in an $8$-minute shower is
$$
8(7-2.5)=56-20=36\text{ gallons}
.$$Hence, $36$ gallons of water are saved with the new shower head.
