The formula of a circle is (x-h)^2+(y-k)^2=r^2, where (h,k) is the center. Since (-7,-1) is the center, we have (x+7)^2+(y+1)^2=r^2. To find the radius, we need to find the distance between (-7,-1) and (8,7). Using the distance formula, we get the radius is 17 (make a right triangle with height 8 and base 15). Now, we have (x+7)^2+(y+1)^2=289. Plug in -15 for x and we have (y+1)^2+64=289. (y+1)^2=225. y+1=+-15. y=14, -16. So the Y is 14 and -16.