Ernie's Earmuffs produces 200 earmuffs per year at a totoal cost of $2000 and $400 of its cost is fixed. If he increases output to 220 earmuffs, his total cost increases to $2,100, and his fixed cost remains $400.00 What is Ernie's marginal cost per earmuff?
a. $9.55
b. $35.00
c. $5.00
d. $105.00