Trick for the future:
When finding H+ or OH- from pH or pOH, all you need to type into your calculator is:
2nd log - (pH or pOH) to get the answer
For this problem, you would do 2nd log -(3.4) to get an answer of 3.98 x 10 ^ -4 ≈ 4.0 x 10 ^ -4 like the person above said
