Complete the square on the x and y terms to get
= 16
Then the center is (-2,-5/2) and the radius is 4.
I intentionally omitted the steps in completing the square because of my prior experience with limitations of the current editor for math symbols. But here are some hints:
First divide the 8 out of the x terms and the y terms; this gives you the 46/8 in the second line above.
To complete the square in the x terms, you add 4 and in the y terms you add 25/4. You should now be able to follow the answer.
If you are still stuck, please send me a message and I will try to help further.