How would one set this word problem as an equation?

A piece of wood burns completely in one second at 600C. The time the wood takes to burn is doubled for every 10C drop in temperature and halved for every 10C increase in temperature. In how many seconds would the wood burn at

a) 500C b)650C

I've just gotten started working with exponents so I only have a basic understanding of the doubling function, and that doesn't help much...