A company uses four hours of direct labor to produce one unit. The standard direct labor cost is \(\$ 20\) per hour. This period the company produced 20,000 units and used 84,160 hours of direct labor at a total cost of \(\$ 1,599,040\). What is its direct labor rate variance for the period?
a. \(\$ 83,200 \mathrm{~F}\)
b. \(\$ 84,160 \mathrm{U}\)
c. \(\$ 84,160 \mathrm{~F}\)
d. \(\$ 83,200 \mathrm{U}\)
e. \(\$ 960 \mathrm{~F}\)