Afirm is considering which of two mechanical devices to install to reduce cost devices a and b have service lives of 5 and 10 years. respectively device a costs $1,200 and can be expected to result in $400 savings annually. device b costs $1,500 and will provide cost savings of $325 the fist year but will increase $40 annually making second year savings $365 , the third year savings $405 and so forth. salvage values for devices a and b are $100 and $150 respectively. with interest at 5% which device should the firm purchase