Hi,
I would say that the answer is 28, but it still doesn't add up because when you multiply 12 by 28 you get $3.36 which isn't enough to meet his total, so I tried multiplying 12 by 29 and I got $3.48, which is six cents over his total. So I'm sorry if it is wrong I tried to help to my best ability.
I hope it helps, have a great day/night!!!