For the cracking reaction shown below, calculate the fraction of propone, $C_3H_8$, that reacts if the equilibrium constant, $K = 2$. You can assume that the reaction takes place in the gas phase at standard pressure, but you should state any further assumptions that you make.

$C_3H_{8(g)} \leftrightarrow C_2H_{4(g)} + CH_{4(g)}$