Answer:
$3.50
Explanation:
first you take the amounts you do know, which is the total amount and the cost of one order of fries.
you know he got 2 fries, so thats 1.50 times 2.
1.50 x 2 = 3.00
then you subtract that from the total
6.50 - 3.00 and you're left with 3.50