Dont get these two questions! Having a hard time please help! Thank youuu! :)

17) Dure Corporation's cost formula for its selling and administrative expense is $24,500 per month plus SI per unit. For the month of July, the compa planned for activity of 7,200 units, but the actual level of activity was 7,160 units. The actual selling and administrative expense for the month was S31,460 The selling and administrative expense in the planning budget for July would be closest to: A) S31,460 B) S31,700 C) $31,636 D) S31,660 18) Dure Corporation's cost formula for its selling and administrative expense is $24,500 per month plus S1 per unit. For the month of July, the compa planned for activity of 7,200 units, bt the actual level of activity was 7,160 units. The actual selling and administrative expense for the month was 31,460. The selling and administrative expense in the flexible budget for July would be closest to: A) $31,460 B) S31,700 C)$31,660 D) $31,524