The following information applies to the questions displayed below.$]$

Data for Hermann Corporation are shown below:

Per Unit Percent of Sales

Selling price $ $120100\%$

Variable expenses $7865$

Contribution margin $ $4235\%$

Fixed expenses are $$84,000$ per month and the company is selling $2,600$ units per month.

Required:

$1-$a$.$ How much will net operating income increase $($decrease$)$ per month if the monthly advertising budget increases by $$8,900,$ the monthly sales volume increases by $100$ units, and the total monthly sales increase by $$12,000?$

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