How would I solve problem 9? Please show steps!

9, Danson & Highsmith LLC expects the following results for the next accounting period: Sales Variable costs Fixed costs Expected production and sales in units S390,000 $187,200 $124,000 5,200 The sales manager believes sales could be increased by 900 units if advertising expenditures were increased by $17,000. If advertising expenditures are increased and sales increase by 900 units, the effect on, operating income will be a(n) Decrease of $18,100 b. Decrease of $35,100 c Increase of $18,100 Increase of $35,100