Armstrong Production Company has the following information:

Standard fixed factory overhead rates per direct labor$-$hour $$1\mathrm{.}50$

Standard variable factory overhead rates per direct labor$-$hour $$5\mathrm{.}00$

Actual number of units produced $4,800$ units

Actual factory overhead costs$*$ $$62,400$

Actual direct labor hours $4,800$ hours

$*($includes $$56,000$ fixed$)$

Standard factory overhead rates are based on a normal monthly volume of $4,000$ units $(1$ standard direct labor$-$hour per unit$).$

What is Armstrong's variable overhead efficiency variance?

Select one:

a$.$

$$800($F$)$

b$.$

$$4,000($F$)$

c$.$

$$0$

d$.$

$$4,800($U$)$