Well, you would find the pOH using pOH= -log(OH-), then you would subtract that answer from 14, as pH + pOH = 14 :) Since you are only given [OH], you HAVE to find pOH first.
In this example, you would do pOH =
Next, you know that pOH + pH = 14 so you sub in pOH....
3.08 + pH = 14 --> solve for pH
pH = 14 - 3.08
pH = 10.92
Therefore, the pH is 10.92