8.2 When the monopolist expands from 3 to 4 units per week, total revenue rises from $15 to $16 per week, which means that the marginal revenue from the sale of the fourth unit is only $1 per week. When the monopolist expands from 4 to 5 units per week, total revenue drops from $16 to $15 per week, which means that the marginal revenue from the sale of the fifth unit is actually negative, or −$1 per week. (LO4)