The marginal revenue of selling the eighth unit is $-4.
A monopolist is the only producer in the industry. A monopolist operates in a monopoly. The monopolist sets the market price of their products.
Marginal revenue is the change in total revenue when quantity sold increases by one unit.
Marginal revenue = change in total revenue / change in quantity sold
change in total revenue = ($3 x 8) - ($4 x 7) = $-4
change in quantity sold = 8 - 7 = 1
Marginal revenue = $-4 / 1 = $4
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