Feather Friends, Inc., distributes a high-quality wooden bird houses that sells for $80 per unit. Variable expenses are $40 per unit. Fixed expenses total $180,000 per year.

Assume the company sold 36,000 units last year. The president does not want to change the selling price. Instead, he wants to increase the sales commission by $1.60 per unit. He thinks that this move, combined with some increase in advertising, would double annual unit sales. By how much could advertising be increased with profits remained unchanged? Use incremental analysis approach.