The AAA Aquarium Co. sells aquariums for $20 each. Fixed costs of production are $20. The total variable costs are $20 for one aquarium, $25 for two units, $35 for three units, $50 for four units, and $80 for five units. In the form of a table (use Table 8.7 for reference), calculate total revenue, marginal revenue, total cost, and marginal cost for each output level (one to five units). What is the marginal cost for 4 aquariums? ~