The following data is given for the Bahia Company:

Budgeted production	1,000 units
Actual production	980 units
Materials:
Standard price per pound	$2.00
Standard pounds per completed unit	12
Actual pounds purchased and used in production	11,800
Actual price paid for materials	$23,000
Labor:
Standard hourly labor rate	$14 per hour
Standard hours allowed per completed unit	4.5
Actual labor hours worked	4,560
Actual total labor costs	$62,928
Overhead:
Actual and budgeted fixed overhead	$27,000
Standard variable overhead rate	$3.50 per standard labor hour
Actual variable overhead costs	$15,500

Overhead is applied on standard labor hours. Question: The factory overhead volume variance is

540 unfavorable

Could you explain why?