The formula of a midpoint:
[tex]M_{ST}\left(\dfrac{x_S+x_T}{2},\ \dfrac{y_S+y_T}{2}\right)[/tex]
We have:
[tex]T(0,\ 4)\to x_T+0,\ y_T=4\\M(7,\ -5)\to x_M=7,\ y_M=-5[/tex]
Substitute:
[tex]\dfrac{x_S+0}{2}=7\qquad|\cdot2\\\\x_S=14\\\\\dfrac{y_S+4}{2}=-5\qquad|\cdot2\\\\y_S+4=-10\qquad|-4\\\\y_S=-14[/tex]
Answer: S(14, -14).
