$8.70 is the total cost without the coupons. He gets 6 gallons. He gets $0.55 off per gallon.
To find the total price Zak got off, multiply 6 and $0.55. 6 x $0.55 = $3.30, so he got $3.30 off.
To find the total price. Add the total cost without the coupons + the amount the coupons saved him.
$8.70 + $3.30 = $12
To find the price per one gallon, divide the total price / number of gallons
$12/6 = $2. The regular price is $2 a gallon