First, subtract px2 from both sides.
Now you have:
x3 - px2 = (1 - p) x1
Next, divide both sides by (1 - p)
So now you have
x3 - px2/(1 - p) = x1
...as your final answer
*You can decide if you want to leave the parenthesis in your final answer, I left them there so it could be visible where I put them. :)
