In the standard \((x,y)\) coordinate plane, the point \((2,1)\) is the midpoint of \(\overline{CD}\). Point \(C\) has coordinates \((6,8)\). What are the coordinates of point \(D\) ?

\(\displaystyle \left(-2,-\frac{7}{2}\right) \)

\(\displaystyle \left(-2,-6\right)\)

\(\displaystyle \left(4,\frac{9}{2}\right) \)

\((10,10)\)

\((10,15)\)