The center has coordinates h = -2, k = 5. The radius is sqrt(6). The equation for a circle is as follows:

. Filling in using our given info we have

. Simplifying that down we have an equation of

. There you go!
Answer:
-1.5
Step-by-step explanation:
The distance between S and T is
4 - -7
4+7 = 11
Divide this in half to find the midpoint
11/2 = 5.5
Add this to point S to get the point itself
-7 + 5.5 = -1.5