$\mathrm{A}(-2,4), \mathrm{C}(4,10)$ and $\mathrm{D}\left(-2,10\right)$ are the vertices of a square $\mathrm{ABCD}$. Use graphical method to find the coordinates of the fourth vertex $\mathrm{B}$. Also, find 

the coordinates of the point of intersection of the diagonals of the square $\mathrm{ABCD}$.