Correct Answer - Option 2 : 31

The logic followed here is,

Square root of the first number and second number then adding the both results i.e.,

I → \(\sqrt {324} \) + \(\sqrt {289} \) = 18 + 17 = 35

II → \(\sqrt {400} \) + \(\sqrt {49} \) = 20 + 7 = 27

Similarly, III → \(\sqrt {484}\) + \(\sqrt {81}\) = 22 + 9 = 31

Therefore, 31 is the correct answer.