At the end of the accounting period Stanley, Inc. reports operating income of $24,000, a contribution margin of $12 per unit, and a fixed overhead rate of $4 per unit. Under variable costing, if this company produces 50 more units of inventory, then operating income:

a. will increase by $400

b. will increase by $200

c. will decrease by $600

d. will decrease by $400

e. will decrease by $200

f. will increase by $600

g. will not be affected

h. Cannot be determined