What is the undefined value for 22=4+ [5x/9x−6]?

To find the undefined value for the equation

\[
22 = 4 + \frac{5x}{9x - 6},
\]

we need to determine when the fraction \(\frac{5x}{9x - 6}\) is undefined. A fraction is undefined when its denominator is equal to zero. Thus, we set the denominator equal to zero and solve for \(x\):

\[
9x - 6 = 0.
\]

Adding 6 to both sides gives:

\[
9x = 6.
\]

Now, dividing both sides by 9:

\[
x = \frac{6}{9} = \frac{2}{3}.
\]

So, the undefined value for \(x\) is

\[
\frac{2}{3}.
\]

Thus, the answer is:

\[
\frac{2}{3}.
\]