From the equation Pv = n RT for the two gases. We can write
0.8 x 0.5 = nH2 x RT or nH2 = 0.8 x 0.5 / RT
ALSO 0.7 x 2.0 = n02 . RT or n02 = 0.7 x 2 / RT
When introduced in 1 L vessel, then
Px1L = (n02 + nH2) RT
Putting the values, we get
P = 0.4 + 1.4 = 1.8 bar
Hence, the total pressure of the gaseous mixture in the vessel is 1.8 bar