Per Unit Percent of Sales

Selling price $ $55100\%$

Variable expenses $3360$

Contribution margin $ $2240\%$

Fixed expenses are $$71,000$ per month and the company is selling $4,100$ units per month.

Required:

$1-$a$.$ How much will net operating income increase $($decrease$)$ per month if the monthly advertising budget increases by $$9,500,$ the monthly sales volume increases by $100$ units, and the total monthly sales increase by $$5,500?$

$1-$b$.$ Should the advertising budget be increased?