Trey, Amelia, and Cho are discussing the solution set to the equation x2+9=45.

To solve the equation \(x^2 + 9 = 45\), we first isolate \(x^2\):

\[
x^2 = 45 - 9
\]

\[
x^2 = 36
\]

Next, we take the square root of both sides:

\[
x = \pm \sqrt{36}
\]

\[
x = \pm 6
\]

This means the solution set is \(\{-6, 6\}\).

Among the responses:

- Trey says the solution is \{6\} - Incorrect.
- Amelia says the solution is \{-6, 6\} - Correct.
- Cho says the solution is \{-6\} - Incorrect.

Thus, the correct answer is:

**Amelia**.