Please can you write the solution by hand . Im not sure why some solutions have the 1st cost as positive and then salvage value as negative can you please explain why they do this too . Thank you

26 Westmount Waxworks is considering buying a new wax melter for its line of replicas of statues of government leaders. There are two choices of supplier, Finedetail and Simplicity. Their proposals are as follows: Management thinks the company will sell about 30000 replicas per year if there is stability in world governments. If the world becomes very unsettled so that there are frequent overturns of governments, sales may be as high as 200000 units a year. Westmount Waxworks uses a MARR of 15 percent for equipment projects. (a) Who is the preferred supplier if sales are 30000 units per year? Use an annual worth comparison. (b) Who is the preferred supplier if sales are 200000 units per year? Use an annual worth comparison. (c) How sensitive is the choice of supplier to sales level? Experiment with sales levels between 30000 and 200000 units per year. At what sales level will the costs of the two melters be equal