We know that:

is an equation of a circle.
When we substitute x and y (from the pairs we have), we'll get a system of equations:

and all we have to do is solve it for a, b and r.
There will be:

From equations (II) and (III) we have:

and from (I) and (II):

Now we can easly calculate a and b:

Finally we calculate

:

And the equation of the circle is:
-7=z/2+1
What you first need to do is to multiply both sides of the equation by 2
-14=z+2
Now you move the variable to the left side and change within it’s own sign
-z-14=2
Into
-z=2+14
Now you then add the numbers
-z=16
The last part you do is change the sign on both sides in this equation
z=-16
Therefore, z=-16 is your answer in number 16.
-24n - 30, i suggest using math.way before asking a math question aha