Which cost more per issue, an 18-issue subscription for $40.50 or a 12-issue subscription for $33.60?

So what you would do is you would dived the subscriptions by the cost 
Soo...

$40.50/18 =2.25
$33.60/12=2.80

so therefore 12 issue subscriptions for $33.60 would be more 

Your answer should be 1/3. i hope i could ! good luck : )