Winners from last weeks math problem, and the new problem of the week

The Digit Problem ANSWER:  9
Winners: Riker Barton, Dexter Bradford, Tiffany Chan, Sara Chandler, Ethan Graham, Xander Henry, Spencer Huffaker, Corbin Jensen, Garyn Jensen, Callie Johnson, Maddy Johnson, Tracee Jones, Noah Lane, JJ Marsigli, Ethan Oyler, Jordyn Pearson, Morganne Price, Naomi Rawlins, Ty Reese, David Riding, Aspen Seamons, Tyler Thompson

The Subway Wheels Problem

The New York City subway system buys wheels for their subway cars for $200 per wheel.  The wheels last for ten years. And then they have a scrap value of $25 apiece.  If rust-proofing treatment costing $50 a wheel is applied, each wheel will last fifteen years but will have not scrap value.  In the long run, would it be more cost effective to rust-proof the wheels or not?