We know,
Molar mass=2×Vapour density
Molar mass of mixture=2×28.75=57.5
Number of moles in 100 g of mixture=10057.5
Let a g of NO2 is present in mixture.
Moles of NO2+Moles of N2O4=Moles of mixture
a46+100−a92=10057.5⇒100+a=100×9257.5⇒a=60 g
Moles of NO2 in mixture=6046=1.30