$5.$ Refer to the original data. During the first year, the store sold only $2,500$ pairs of sandals and reported the following operating results:

Sales $(2,500$ pairs$)$$ $50,000$Variable expenses$30,000$Contribution margin$20,000$Fixed expenses$16,000$Net operating income$ $4,000$

What is the store$$s degree of operating leverage?

Angie is confident a more intense sales effort and a more creative advertising program will increase unit sales by $50\%$ next year. Using the degree of operating leverage, what would be the expected percentage increase in net operating income if Angie is able to increase unit sales by $50\%?$