Step 1: Add \( 12 + 9i \) to \( z = 1 + i \):
\[
z + 12 + 9i = 1 + i + 12 + 9i = 13 + 10i
\]
Step 2: Now, calculate the modulus:
\[
|13 + 10i| = \sqrt{13^2 + 10^2} = \sqrt{169 + 100} = \sqrt{269}
\]
Step 3: Thus, the maximum value is \( \sqrt{269} \).