To be able to calculate the required values clearly, first let us define the variables one by one.
Number of units manufactured = 20,000 units
Standard hours per unit = 18 minutes / unit = 0.3 hours / unit
Total standard hours = 20,000 units * (0.3 hours / unit)
Total standard hours = 6,000 hours
Standard rate per hour = $12 / hour
Total standard rate = ($12 / hour) * 6,000 hours
Total standard rate= $72,000
Total standard rate = Standard labor cost
Actual direct labor cost is $73,600, therefore there was an excess of $1,600. The variance is unfavorable.