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 \( x^2 \):

1. Subtract 9 from both sides:
\[
x^2 = 45 - 9
\]
\[
x^2 = 36
\]

2. Next, take the square root of both sides:
\[
x = \pm 6
\]

Thus, the solutions to the equation are \( -6 \) and \( 6 \).

Now, examining the options:
- Trey says the solution is {6}. **Incorrect.**
- Amelia says the solution is {−6, 6}. **Correct.**
- Cho says the solution is {−6}. **Incorrect.**

Therefore, Amelia has found the correct solution set.

The answer is:
**Amelia**