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