We are given that "x" and "y" vary inversely. This means that the variables follow the next relationship:

Where "k" is a constant to be determined. To determine "k" we will use the given values:

Now, we plug in the values:

Now, we solve for "k" by multiplying both sides by 3:

Therefore, the value of "k" is 18. Now, we substitute in the relationship:

And thus we get the equation.