Ask yourself this question:

What does the denominator, 7, on the left of the equal sign
have to be multiplied by to get the denominator, 49, on the right
of the equal sign?

The answer is 7, since 7 times 7 is 49.

Now ask yourself another question.

How do you make 1 using two 7's?

Answer: put one seven over the other, like this 

So multiply  by , which changes the looks of
the fraction , but it cannot change the value because 
multiplying by 1 cannot change the value, just the looks:



So the number that goes where the question mark is, is 42.



Edwin