Acompany uses four hours of direct labor to produce a product 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 labor rate variance for the period?

a. $83,200 F

b. $84,160 U

c. $84,160 F

d. $83,200 U

e. $ 960 F