Need help with #12 pls explain

The center of the circle is just the ordered pair...so it would be (2,-3). To find the radius you start at the center and count to the right until you reach the edge of the circle. (You could also count to the left). So your radius would be 2. I’m not sure on the equation

Y = 2x + 5
x + 2y = 15

    x + 2(2x + 5) = 15
x + 2(2x) + 2(5) = 15
      x + 4x + 10 = 15
            5x + 10 = 15
                  - 10 - 10
                     5x = 5
                      5     5
                       x = 1
y = 2(1) + 5
y = 2 + 5
y = 7
(x, y) = (1, 7)