#18. how is the answer -3. how do i get it?

7m+3(m+2)=-24
Distribute
3(m+2)=3m+6
7m+3m+6=-24
Combine like terms
7m+3m=10m
10m+6=24
Do the additive inverse of addition
-24-6=
Do keep change change
-24+-6=-30
10m=-30
Do the inverse of division/multiplication
the m cancels out
-30÷10=-3
because a negative divided by a positive equals a negative the result is -3
this is why it is -3.

The standard equation of a circle is:

(x-h)^2+(y-k)^2=r^2, where (h,k) is the center of the circle and r is the radius.

We are given two endpoints of the diameter, so the midpoint of these points is the center of the circle.  (2,8) and (2, -4)  so the midpoint of the circle is:

((2+2)/2, (8-4)/2)

(2,2)

The radius is just half the length of the diameter.  The length of the diameter is 8--4=12 so the radius is 6 units, so our circle equation is:

(x-2)^2+(y-2)^2=36