Answer:
3x:4x for some real number x
Explanation:
Since answer choices weren't provided, I generalized my answer.
First, notice we can simplify 6:4 into 3:2 because we can write the ratio as a fraction and simplify (6 and 4 are both multiples of 2).
Since 3 and 2 are relatively prime and the ratio cannot simplify anymore, we can say that the ratio of 6:4 = 3:2 = 3x:2x for some real number x because we can see that 3x:2x = 3:2 by simplifying (3x and 3 are both multiples of x).
As long as the answer choice you choose matches the format above, you should be correct! I hope this helps! :)