A monopolist's marginal revenues for each of the first eight units that it produces are. respectively; $28, $23, $18, $13, $8, $3, -$2 and -$7 per unit. The marginal costs of producing these same eight units are. respectively; $2, $3, $4, $5, $6, $7, $8 and $9 per unit. What is the smallest per product unit subsidy that must be paid to the monopolist in order to induce it to produce 7 units of its product?