If 9 is to 3, what is 18 to?

To understand the relationship in the analogy presented, we can look at the mathematical operation involved. The first pair is 9 and 3, where we can see that 9 divided by 3 equals 3.

Now, applying the same operation for the second pair, we start with 18. If we want to find what it is to in relation to 3, we would divide 18 by 3, which gives us 6. Thus, if 9 is to 3 as 18 is to 6, the answer correctly corresponds to the choice that indicates 6.

This demonstrates a direct proportional relationship between the pairs, where the first number is divided by the second number to yield a consistent result.