To solve the equation \( z^2 = 264.950495290000 \), we need to take the square root of both sides.
1. Take the square root of 264.950495290000:
\[
z = \sqrt{264.950495290000}
\]
2. Using a calculator to find the square root:
\[
z \approx 16.28
\]
3. Rounding to the nearest tenth:
\[
z \approx 16.3
\]
Thus, the solution is:
\[
\boxed{16.3}
\]