Mindy, a local artist, sells a piece of art at the pizza shop for $15, and the shop takes 15 percent commission. instead of receiving money, mindy would like a $12 pizza, including 5 percent sales tax. is this a fair trade? explain how to find the solution.

In this question the first thing that needs to be determined is the commission taken by the pizza shop and the amount of money that falls in the part of Mindy.
We already know that Mindy sells the piece of art for $15 and the pizza shop takes 15% commission on it.
Then
Commission taken by the pizza shop = (15/100) * 15
                                                             = 225/100
                                                             = 2.25 dollars
So the pizza shop takes a commission of $2.25 from the sales of each art piece from Mindy.
Then amount that falls in Mindy's part = (15 - 2.25) dollars
                                                             = 12.75 dollars
Now Mindy is not taking the money but taking a pizza worth rupees $12 including 5% sales tax.
Initially it looks like Mindy is making a profit of $0.75 plus the pizza worth $12. So it is a fair deal for Mindy. Now coming to the part of the pizza shop owner, we find that he also gains extra $2.25 from this deal. So it is a fair deal for both the shop keeper and Mindy.