It's balanced. The coefficients create 4 H and 4 O on the left side and 4 H and 4 O on the left. You basically just do 2 times 2 for the H2 on the left side and 2 times 2 for the O2 on the left side and for the right you do 2 times H2 on the right which makes it 4, 2 Times O which makes 2 plus the O2 that you have aswell
