Final answer:
Charlie can spend no more than $5.60 on each sandwich.
Step-by-step explanation:
To find out how much Charlie can spend on each sandwich, we need to divide his total budget by the number of sandwiches he wants to order. In this case, Charlie has $28 and wants to order 5 sandwiches, so we divide $28 by 5. This gives us an answer of $5.60 per sandwich, which means Charlie can spend no more than $5.60 on each sandwich.