BackFill Systems allocates manufacturing overhead based on machine hours. Each connector should require 13 machine hours. According to the static budget, BackFill expected to incur the following:

1,300 machine hours per month (100 connectors * 13 machine hours per connector)

$6500 in variable manufacturing overhead costs

$5550 in fixed manufacturing overhead costs

During August, BackFill actually used 400 machine hours to make 85 connectors and spent $5,500 in variable manufacturing costs and $8800 in fixed manufacturing overhead costs. Calculate the variable overhead efficiency variance for BackFill.

a. $3,525 F

b. $3,500 U

c. $25 F

d. $7,025 F