The correct expression for determining the total cost of buying pounds of for $ per pound and pounds of for $ per pound is:
4.85 m + 0.82 s
This expression represents the cost of buying m pounds of at a cost of $4.85 per pound, plus the cost of buying s pounds of at a cost of $0.82 per pound.
The other options do not accurately represent the total cost of buying these two types of products. Option A multiplies the total number of pounds bought (m+s) by the cost per pound of one of the products, but does not take into account the different costs per pound of the two products. Option B adds the cost of buying m pounds of to the cost of buying s pounds of , but does not use the correct costs per pound for each product. Option D subtracts the cost of buying s pounds of from the cost of buying m pounds of , which does not accurately represent the total cost of buying both products.