The following information was taken from the annual manufacturing overhead cost budget of Fergie Manufacturing.

Variable manufacturing overhead costs $$92,400$

Fixed manufacturing overhead costs $$55,440$

Normal production level in labor hours $23,100$

Normal production level in units $5,775$

Standard labor hours per unit $4$

During the year, $5,600$ units were produced, $18,340$ hours were worked, and the actual manufacturing overhead was $$151,200.$ Actual fixed manufacturing overhead costs equaled budgeted fixed manufacturing overhead costs. Overhead is applied on the basis of direct labor hours. Fergie's volume overhead variance is:

a$.$ $$1,680$ U$.$

b$.$ $$6,160$ U$.$

c$.$ $$7,840$ U$.$

d$.$ $$22,400$ U$.$