Matt and Kristin are newly married and living in their first house. The yearly premium on their homeowners insurance policy is $500 for the coverage they need. Their insurance company offers a 3 percent discount if they install dead-bolt locks on all exterior doors. The couple can also receive a 1 percent discount 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 $45 each. At the local hardware store, smoke detectors cost $9 each, and the new house has two floors. Kristin and Matt can install them themselves.

Assuming their insurance rates remain the same, how many years will it take Matt and Kristin to earn back in discounts the cost of the dead bolts? The cost of the smoke detectors?