Xero Company's standard factory overhead rate is $3.75 per direct labor hour (DLH), calculated at 90% capacity = 900 standard DLHs. In December, the company operated at 80% of capacity, or 800 standard DLHs. Budgeted factories overhead at 80 percent of capacity is $3,150, of which $1,350 is fixed overhead. For December, the actual factory overhead cost was $3,800 for 840 actual DLHs, of which $1,300 was for fixed factory overhead. Suppose the use of a two-way breakdown (decomposition) of the total overhead variance, Find the factory overhead efficiency variance for December?