Answer:
Either 12/16 or 9/12
Explanation:
Since you are including 12 then both the numerator and denominator of the equation must be multiplied to become a proper representation of the original fraction. For instance:
If you have a/b and you change a to be 12 then b must be (12/a)b and vice versa for the other. In this example, you have 3/4 where you're replacing one with 12 so let's do the first:
12/3=4 so the denominator is equal to 4*4=16 or (12/a)b as mentioned before.
Then we have to do it to the other since the question didn't specify which element we are substituting:
12/4=3 so the numerator is equal to 3*3=9 or (12/b)a.
Hope this helps. Comment if you have a question.