Ken paid $12 for two magazines. the cost of each magazine was a multiple of $3. what are the possible prices of the magazines?

Two possible prices are 9 dollars and 3 dollars. 9 is a multiple of 3 and 3 is a multiple of three 9+3 is 12. you can also do 6 and 6. 6 is also a multiple of three and 6+6 is 12