Standards specify 0.1 direct labor hours per unit of product. At the beginning of the year, the static budget for variable overhead costs included the following data:

Production volume………………………6,000 units

Estimated variable overhead costs………$13,500

Estimated direct labor hours (Dh?r)…….600 hours

At the end of the year, actual data were as follows:

Production volume………………………4,000 units

Actual variable overhead costs………….$15,000

Actual direct labor hours (Dh?r)………..480 hours

Calculate the variable overhead efficiency variance.