I need help with Req 6

Feather Friends, Inc., distributes a high-quality wooden birdhouse that sells for $120 per unit. Variable expenses are $60.00 per unit, and fixed expenses total $200,000 per year. Its operating results for last year were as follows:

Sales	$	3,120,000
Variable expenses		1,560,000
Contribution margin		1,560,000
Fixed expenses		200,000
Net operating income	$	1,360,000

Required:

6. The president does not want to change the selling price. Instead, he wants to increase the sales commission by $2.30 per unit. He thinks that this move, combined with some increase in advertising, would increase this year's sales by 25%. How much could the president increase this year's advertising expense and still earn the same $1,360,000 net operating income as last year? Do not prepare an income statement; use the incremental analysis approach.