EXPLANATION
Assuming that p represents the pairs of pants and s represent the shirts, we can apply the following reasoning:
28p +11(p + 5)
Shirt cost (s) = $11
Pairs of pants cost (p) = $28
The term 28p represent the cost for p pants at $28 each.
The term 11(p+5) represents the cost for the shirts at $11 each.
The term 28p + 11(p + 5) represents the total cost for the shirts and pants that Chris bought.