Assume that the best cost driver that Sony has for variable factory overhead in the assembly department is machine hours. During April, the company budgeted 580,000 machine hours and $6,000,000 for its Texas plant's assembly department. The actual variable overhead incurred was $6,200,000, which was related to 600,000 machine hours. (Round your answers to the nearest dollar. Do not round until your final answers.) a) determine the variable overhead spending variance b) determine the variable overhead efficiency variance