A manufacturer of pick-up trucks popular with construction contractors and landscaping businesses offers three new models of their best-selling truck. The first uses steel panels for the body work. The second uses aluminum, and costs $2.500 more but weighs 300 kg less. The third offers carbon-fiber paneling, costs $8,000 more and weighs 500 kg less. All else remaining the same, based on cost and weight, which one is the best purchase? Construction contractors and landscaping business are eager to save weight so the exchange constant can be taken to be $20/kg