The normal capacity of Noel Company is 4,000 units per month. At this volume, budgeted fixed and variable factory overhead are $16,000 and $20,000, respectively. In May, actual production was 4,200 units and actual overhead incurred was $37,900. What is the variance between budgeted factory overhead per the flexible budget and actual overhead incurred?

a. $1,000 U

b. $900 U

c. $100 U

d. $1,900 U