Shamrock Company's overhead rate was based on estimates of $186,000 for overhead costs and 18,600 direct labour hours. Shamrock's standards allow 2 hours of direct labour per unit produced. Production in May was 800 units, and actual overhead incurred in May was $19,000. The overhead budgeted for 1,600 standard direct labour hours is $15,850 ( $4,650 fixed and $11,200 variable). (a) Calculate the total, budget, and volume variances for overhead