The Lewis Corporation specializes in manufacturing one type of desk lamp. The company allocates variable manufacturing overhead costs on the basis of machine hours. Lewis Corp budgeted 0.3 machine hours per lamp and allocates overhead at a rate of $1.50 per machine hour. Last year Chilton manufactured 24,000 lamps, used 12,000 machine hours and incurred actual overhead costs of $16,800. What was Lewis Corp's variable manufacturing overhead efficiency variance last year?

A) $1,200 favorable

B) $7,200 unfavorable

C) $7,200 favorable

D) $1,200 unfavorable