C. 33%
First you have to find the amount spent with the gift card.
41.09 - 27.74 = 13.35
$13.35 was spent with the gift card.
Now you have to find the percentage that 13.35 is of 41.09
13.35/41.09 = 0.324896568508153
0.324896568508153 x 100 = 32.48965685081528
32.48965685081528 would round up to 33
Therefore, the percentage that best describes the part of the total that Carson paid for with the gift card is 33%