In the first quadrant the signs would be (x,y) in the second quadrant they would be (-x,y) in the third (-x,-y) and the fourth (x,-y)
We know that Ava is paying $2 dollars per week so if L is the money that she owes and t is the number of weeks, and I is the initial debt so we can write an equation like:

Now we can replace the info we have to find the value of I so:

and we solve for I

So the final equation will be:
Answer:
Center: (-5,10)
Radius: 2
Step-by-step explanation:
The equation of the circle in center-radius form is:

Where the point (h,k) is the center of the circle and "r" is the radius.
Subtract 121 from both sides of the equation:

Add 10x to both sides:

Make two groups for variable "x" and variable "y":

Complete the square:
Add
inside the parentheses of "x".
Add
inside the parentheses of "y".
Add
and
to the right side of the equation.
Then:

Rewriting, you get that the equation of the circle in center-radius form is:

You can observe that the radius of the circle is:

And the center is:

I hope this helps you
56+35+CB=180
CB=91
AE=117
AEC=180+56=236
BDA=89+56+180=325