To evaluate the expression \( 3.3 - 0.7z \) for \( z = 9 \), we first substitute \( z \) with 9:
\[ 3.3 - 0.7(9) \]
Next, we calculate \( 0.7 \times 9 \):
\[ 0.7 \times 9 = 6.3 \]
Now, we can substitute this back into the expression:
\[ 3.3 - 6.3 \]
Next, we perform the subtraction:
\[ 3.3 - 6.3 = -3.0 \]
Thus, the final result is:
\[ \boxed{-3} \]