Dear Student,
Please find below the solution to your problem.
Let x grams of each hydrogen and methane are mixed,
Moles of H2 = x/2
Moles of CH4 = x/16
⇒ Mole-fraction of H2 = (x/2)/(x/2 + x/16)
= 8/9
⇒ (Partial pressure of H_2)/(Total pressure)
= mole-fraction of H2
= 8/9
Thanks and Regards