If isobutane and n-butane are present in a gas, then how much oxygen should be required for complete combustion of 5 kg of this gas

Isobutane  and  n−butane  C4H10  have same  molecular  formula;C4H10 +  132  O2  → 4CO2+5H2O        58  g  of  C4H10 require→ 208  g of  O2 5×103g of  C4H10 require→         ?C4H10  required  =  5×103 ×  20858=17.9×103g=17.9Kg