Explain how to do these questions.

Here, Each raw and Column has it's own pattern.

In 2nd column, You can see numerators are multiple of 3, and denominators of 12, so it could be anything which relate them:

Like 1/12, 3/48, 5/100, 7/168

In the same pattern in 1st column, numerators are constant & denominators are multiples of 14, 

So, 3/7, 3/14, 3/35, 3/70

[ Do with the same pattern for whole Grid ]

Hope this helps!