Please see question below?

Question

A gas mixture contains twice as many moles of O2 as N2. Addition of 0.200 mol of argon to this mixture increases the pressure from 0.800 atm to 1.10 atm. How many moles of O2 are in the mixture?

I don't even know how to setup the problem. Can somebody help me please!?

The first answer provided is not correct. Can someone please help me?

Answer 1

Let moles of N2 = x

Moles of O2 = 2x

Now, 0.2*1.1/(x+2x+0.2) = 1.1-0.8 = 0.3

So, 2.2 = 9x + 0.6

or x = 1.6/9 = 0.178

Thus moles of O2 = 0.356.