The following standards for variable overhead have been established for a company that makes only one product: The following data pertain to operations for the last month: Required: a. What is the variable overhead rate variance for the month? b. What is the variable overhead efficiency variance for the month? (Indicate the effect of each variance by selecting "F" for favorable, " U " for unfavorable, and "None" for no effect (i.e., zero variance). Input all amounts as positive values.)