Extreme Builders constructs houses. The standard labor rate is $25 per hour and the standard number of hours is 15,000 hours per home. During the year, it constructed 12 homes using 18,000 labor hours per home and a rate of $28 per hour. Calculate the Extreme Builders' labor rate variance.

a.$648,000 F

b.$648,000 U

c.$540,000 U

d.$540,000 F