Steel is an alloy of C in Fe$.$ The carbon atoms are interstitial, and Fe is BCC$.$ If the composition of a steel alloy is $0\mathrm{.}2$ wt$\%$ C$,$ what fraction of unit cells have a carbon atom in them? $($HINT: How many Fe atoms per unit cell? What is the mass of Fe per unit cell? How many Fe unit cells must there be per C atom to yield $0\mathrm{.}2$ wt$\%$ C$?)$

Enter your answer as a decimal.