Equal volumes of $X_{2}$ and $Y_{2}$ gases are allowed to react in a sealed container to form $XY_{3}$ gas.
$X_{2}(g) + 3Y_{2}(g) \rightarrow 2XY_{3}(g)$
After completion of the reaction, the volume of $XY_{3}$ is measured to be $40~cm^{3}$. What was the volume, in $cm^{3}$ of $X_{2}$ gas at the beginning?