Please help figure out this question, Thanks very very much!

Hogle Mfg. Co. uses a standard costing system. The standard time to produce one unit is 4 hours, and normal production is 3,000 units monthly. Overhead costs were estimated to be $135,000. The standard variable overhead rate is $5 per machine hour. During April the following results were recorded: Units produced 3,100 Units sold 2,800 Machine hours required 12,800 Actual overhead costs $136,000 The variable overhead efficiency variance was: Select one: O A. $8,000 U O B. $4,00OU O C. $2,000 U O D. $4,000 F