Dave and Ellen are newly married and living in their first house. The yearly premium on their homeowner's insurance policy is $700 for the coverage they need. Their insurance company offers a discount of 6 percent if they install dead-bolt locks on all exterior doors. The couple can also receive a discount of 3 percent if they install smoke detectors on each floor. They have contacted a locksmith, who will provide and install dead-bolt locks on the two exterior doors for $84 each. At the local hardware store, smoke detectors cost $19 each, and the new house has two floors. Dave and Ellen can install the smoke detectors themselves. a. Assuming their insurance rates remain the same, how many years will it take Dave and Ellen to earn back in discounts the cost of the dead-bolts? (Do not round intermediate calculations. Round your answer to 2 decimal places.) b. How many years will it take Dave and Ellen to earn back in discounts the cost of the smoke detectors? (Do not round intermediate calculations. Round your answer to 2 decimal places.)