Rainy Day Company manufactures umbrellas. Fixed and variable manufacturing cost pools are allocated to each umbrella using budgeted assembly hours. Budgeted assembly time is 4 hours per unit. The following table presents the amounts for July. Required: a. Calculate the efficiency variance for variable overhead costs. b. Calculate the rate variance for variable overhead costs. c. Calculate the rate variance for fixed overhead costs. d. Calculate the production-volume variance for fixed overhead costs