First, you have to add $3.00 and $7.00 because that is what Seth owes as extra (not including the actual cost of the pizzas. So 7+3 equals 10. Then, you have to subtract 10 from the total cost of $64.75 and you end up with $54.75. This is the part where you find out how much each pizza actually was. You have to divide 54.75 by 5. When you do this, you should get an answer of 10.95. This means that each supreme pizza costs $10.95. To check. you multiply 10.95 by 5 which gets you 54.75 and then add the extra charge, the 10 dollars.