To simplify the expression \( \frac{911}{11}z - \frac{411}{11}z \), you can combine the two fractions since they have the same denominator.
We can rewrite the expression as:
\[ \left( \frac{911 - 411}{11} \right) z \]
Now, subtract the numerators:
\[ 911 - 411 = 500 \]
So, we have:
\[ \frac{500}{11}z \]
Thus, the simplified expression is:
\[ \frac{500}{11}z \]