Calcium carbide reacts with oxygen according to the reaction:

$2Ca{C}_2(s)+5O_2(g)2$CaO$(s)+4C{O}_2(g)$

A reaction mixture initially contains $5\mathrm{.}5molCa{C}_2$ and $15\mathrm{.}0mol{O}_2.$

Part A

Once the reaction has occurred as completely as possible, what amount $($in moles$)$ of the excess reactant is Left. Express your answer in moles to one decimar place.