Frank owns an auto repair shop that serves a particular model of auto and so he tends to purchase parts in bulk. Frank is eligible to treat inventory as non-incidental materials and elects to do so. In December of 2019 he purchases 24 oil filters. He uses one to repair an auto in January 2020, and then about 2 per month and ends 2020 with 14 filters. Explain how Frank will treat his oil filter inventory.