The Maxit Corporation has a standard costing system in which variable manufacturing overhead is assigned to production on the basis of standard machine-hours. The following data are available for July:

• Actual variable manufacturing overhead cost incurred: $23,720
• Actual machine-hours worked: 2,100 hours
• Variable overhead rate variance: $4,170 U
• Total variable overhead spending variance: $5,720 U

The variable overhead efficiency variance for July is: