Oslo Company prepared the following contribution format income statement based on a sales volume of $1,000$ units $($the relevant range of production is $500$ units to $1,500$ units$)$:

Sales $ $80,000$

Variable expenses $52,000$

Contribution margin $28,000$

Fixed expenses $21,840$

Net operating income $ $6,160$

Required:

$13.$ Using the degree of operating leverage, what is the estimated percent increase in net operating income that would result from a $5\%$ increase in unit sales?