Final answer:
A rational expression is undefined when the denominator is equal to zero. In this case, the rational expression (z-9)/(6z-54) is undefined when z = 9.
Step-by-step explanation:
A rational expression is undefined when the denominator is equal to zero, as division by zero is undefined in mathematics.
So, to find the values for which the given rational expression, (z-9)/(6z-54), is undefined, we need to set the denominator equal to zero and solve for z.
We have 6z - 54 = 0 ⇒ 6z = 54 ⇒ z = 9.
Therefore, the rational expression is undefined when z = 9.