You did not post up the options, however we can balance this equation ourselves simply by adding multipliers to the front of each reactant and product until all atoms balance. Start with one atom type, say hydrogen, then move to the next and next and keep repeating this process.
2NH3 + O2 ⇒ 2NO + 3H2O
This balances nitrogens and hydrogens, but we still can't balance oxygen, so have to multiply up further
4NH3 + 5O2 ⇒ 4NO + 6H2O
This now balances all 3 atom types for reactants and products.