According to the given picture, we have the following fraction:
18/42
In the fraction 18/42, 18 is the numerator and 42 is the denominator.
To simplify the numerator and denominator to their smallest values we would have to find then the greatest common factor of 18 and 42
To get the greatest common factor we have to divide each number 18 and 42 to a number that is a multiple of the two both numbers.
In this case we divide both 18 and 42 by number 6 and we would see we would whole number for both of them. The result then by dividing the fraction with the number 6 would be equal to 1/3, so
18/42=1/3
That means that by dividing each number 18 and 42 by 6 we would get a whole number, so 6 would be the greatest common factor.