Partridge Co. can further process Product J to produce Product D. Product J is currently selling for $21 per pound and costs $15.75 per pound to produce. Product D would sell for $37 per pound and would require an additional cost of $9.25 per pound to produce. What is the differential revenue of producing Product D? a) $6.75 per pound b) $9.25 per pound c) $16 per pound d) $5.25 per pound