help answer multiple-choice question with explanation please

BE CAREFUL The following is monthly budgeted cost and activity information for two activities in the purchasing department of X Company: Variable Costs Activity Supplier relations Invoicing $8,400 $13,350 Fixed Costs $15,700 $26,100 Cost Driver 300 suppliers 890 invoices In November, actual costs and activity were as follows: Total Costs Activity Supplier relations Invoicing $24,410 $39,138 Driver Amount 316 suppliers 830 invoices What was the flexible budget variance for the invoicing activity for November (assume that favorable variances are positive numbers and unfavorable variances are negative numbers)? A: $-26,688 B: $-25,788 C: $-13,038 D: $-588 E: $0 F: $312