Nobile 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 $35 per pound and would require an additional cost of $8.75 per pound to produce. What is the net differential income of producing Product D?

a. $7 per pound

b. $8.75 per pound

c. $15 per pound

d. $5.25 per pound