Choose the coefficients that balance the reduction halfreact

Choose the coefficients that balance the reduction half-reaction: ?O_2(g) + ?H2O(l) + ?e- ---> ?OH^-(aq). Starting at O_2, the coefficients I got were 1, 2, 4, 4 but the correct answer is 2, 4, 8, 8. Can somebody show me why this is in a step by step process?

Both are correct, 1,2,4,4 is also correct, 2,4,8,8 is just twise of 1.2.4.4