What denominator for 21/3=4/9? would make these ratios proportional

To make the ratios proportional, we need to find a denominator for the fraction 4/9 that would make it equivalent to 21/3.

To find this denominator, we can set up a proportion:

21/3 = 4/9

To balance the proportion, we multiply the numerator and denominator of the left-hand side fraction (21/3) by the same number x:

(21*x) / (3*x) = 4/9

Now, we can see that the denominators of the two fractions (3*x and 9) are already equal. Therefore, the denominator that would make the ratios proportional is 9.