A puzzle like this requires trying many possibilities, and even then you can't be sure the pattern you found is what was intended. There is no general method to teach. (And calculators make no difference.)
What I just did was to factor each number, since it looked like there could be a pattern of that sort, and I noticed that in the first and third columns, the product of the top two numbers equals the product of the bottom two numbers, and that the second column easily fits that pattern. I see no pattern in each row.