He would have bought 5 comics because 3.25 times 5 is 16.25 and after that he is 3.75 left so a good equation for this is 16.25=3.25x because you would take the total he had before entering the book store and minus 3.75 because thats how much he has leftover so you set that to 3.25x because its 3.25 a comic so your tryna find out how many comics he bought that would equal up to 16 dollars and 25 cents.