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 480,000 machine hours and $4,000,000 for its Texas plant's assembly department. The actual variable overhead incurred was $4,180,000, which was related to 500,000 machine hours. Do not round until your final answers. Round your answers to the nearest dollar. (a) Determine the variable overhead spending variance. $ (b) Determine the variable overhead efficiency variance