Millonzi Corporation has a standard cost system in which it applies manufacturing overhead to products on the basis of standard machine-hours (MHs). The company has provided the following data for the most recent month:

Budgeted level of activity	3,600	MHs
Actual level of activity	3,500	MHs
Standard variable manufacturing overhead rate	$6.30	per MH
Actual total variable manufacturing overhead	$21,000

What was the variable overhead rate variance for the month? Please explain so that i can understand it! thanks :)