(6 + 3) + 21 = 6 + (3 + 21)
It's an ASSOCIATIVE PROPERTY
(a + b) + c = a + (b + c)
For this case we must clear x from the given equation:

We passed 23 subtracting the other side of equality:

By definition,
is written as 
So, we have:

So, the solution of
for x is:

Answer:



<h2>
Hello!</h2>
The answer is:
Center: (1,-2)
Radius: 4 units.
<h2>
Why?</h2>
To solve the problem, using the given formula of a circle, we need to find its standard equation form which is equal to:

Where,
"h" and "k"are the coordinates of the center of the circle and "r" is its radius.
So, we need to complete the square for both variable "x" and "y".
The given equation is:

So, solving we have:



Now, we have that:

So,
Center: (1,-2)
Radius: 4 units.
Have a nice day!
Note: I have attached a picture for better understanding.
A complex fraction is a fraction of a fraction