Solutions for imaginary numbers in a+bi

A sample problem is:

Find all solutions of the equation and express them in the form *a* + *bi*.

x^2-7x+13=0

I'm supposed to get 2 answers. A positive conjugate and a negative conjugate.

However when I solve it, I get an odd fraction and the website keeps telling me that this is a wrong answer. And the formatting is right. So I know I'm doing something wrong.

Could someone tell me how these sort of problems are solved? I know most of the steps, but I'm missing something.

Thanks.