Given cos(0) = 5/6
then sin(0) = a/b
Determine the values of a and b.

Total number of T-shirts= 200

Cost per T-shirt (without shipping ) = $2.80

Shipping cost per t-shirt ; 5% of a T-shirt = 0.05 *2.80 = $0.14

Total cost of T-shirt (shipping included) = 2.80 +0.14 = $2.94

Markup = 150% of total cost = 1.50 * 2.94 = $4.41

To get the price at which Michelle will sell each T-shirt , add total cost  to the markup; 2.94 +4.41 = 7.35.

Therefore, selling price will be $7.35