You have to evaluate two devices, WS and DS. WS has an initial cost of $50 per year to operate. It must be completely replaced every 3 years. DS has an initial cost of $200 and costs $30 per year to operate. It must be completely replaced every 5 years. Which device do you recommend if the cost of capital is 10%?

a. DS, the NPV is higher

b. WS, the NPV is lower

c. DS, the EAC is $82.76

d. WS, the EAC is $90.21

e. WS, the EAC is $75.34

Please explain step by step with the necessary formulas.