6-4. Three mutually exclusive design alternatives are being considered. The estimated sales data for Cost Investment cost $30,000 $60,000 $50,000 15,000 20,000 18,000 Estimated units to be sold/ year Unit selling price $3.50 $4.40 $4.10 $/unit $1.00 $1.40 $1.15 Variable costs, $/unit Annual expenses $15,000 $30,000 $26,000 (fixed Market value 0 $20,000 $15,000 Useful life 10 years 10 years 10 years