You have to calculate the cost of the purse + wallet.
First calculate how much Calysia spent, for this you have to subtract the change she got back to the $25.00 she payd:
$25.00-$4.26= $20.74
Now you know that "purse+wallet" cost $20.74, to know how much the wallet costs, you have to subtract the cost of the purse to the total money Calysia spent:
$20.74-$12.99= $7.75
The wallet costed $7.75