Answer:
$11.165 unfavorable 
Step-by-step explanation:
The formula to compute the variable overhead efficiency variance is shown below: 
= (Actual direct labor hours - standard direct labor hours) × variable overhead per hour 
where, 
Actual direct labor hours is 2,975
And, the standard direct labor hours equal to 
= 250 units × 9
= 2,250
Now put these values to the above formula 
So, the value would equal to 
= (2,975 - 2,250) × $15.40
= $11.165 unfavorable