Best Co$.$ can further process Product J to produce Product D$.$ Product J is currently selling for $$21$ per pound and costs $$15\mathrm{.}75$ per pound to produce. Product D would sell for $$35$ per pound and would require an additional cost of $$8\mathrm{.}75$ per pound to produce. What is the differential $($difference$)$ cost per pound of producing Product D$?$

a$.$ $$7$ per pound

b$.***$ $$8\mathrm{.}75$ per pound

c$.$ $$14$ per pound

d$.$ $$5\mathrm{.}25$ per pound info needed found on page $\_\_\_\_\_\_\_\_$