Answer:
You should buy a second t-shirt.
Explanation:
The total without shipping comes out to $65.85. Add the 20% shipping by multiplying .20 by the total, $65.85, and you get $65.85 plus $13.17, the total being $79.02. Now, if you added another shirt for $9.85, your total comes out to $75.70, which barely qualifies for free shipping. In other words, yes, you should purchase a second shirt because you would actually save money, almost $4.