Sun Brite has a new pair of sunglasses it is evaluating. The company expects to sell $6,800$ pairs of sunglasses at a price of $$163$ each and a variable cost of $$115$ each. The equipment necessary for the project will cost $$355,000$ and will be depreciated on a straight$-$line basis over the $7-$year life of the project. Fixed costs are $$290,000$ per year and the tax rate is $24$ percent. How sensitive is the operating cash flow to a $$1$ increase in variable costs per pairs of sunglasses?