joe uses a credit card to buy $396 of groceries and makes no payments for a year. the credit card charges 29% interest. which proportion tells the amount that needs to be added to $396 to find how much he owes in interest at the end of the year?

29/100 = 396/x
x/396 = 29/100
396/29 = x/100
396x/29 = 100/1

Please tell me the bank in which Joe uses because I would love it if the bank only calculated interest once every year.  :-)

But to answer your question, assuming it does then to find interest it would be 

x = 396(.29)

Why on earth they have it written like that is beyond me, but to rewrite the correct answer in the form of your answer choices you it would be
 x/396 = 29/100