Goby fish and shrimp naturally live close together. A pet store is selling bags of goby fish and shrimp to aquarium hobbyists. Each goby fish costs $15, and each shrimp costs $10. Each bag has an equal number of goby fish and shrimp. a. The pet store models the cost per bag with the expression
x(15 + 10)
. Explain what the expression represents.

The expression represents the total cost of the bag which contain x number of goby and x number of shrimp.

b. What other expression can you use to model the cost? Explain what the expression represents.