The diagram above shows Y is the midpoint of line XZ while X is the midpoint of line WZ,
Formula to find the midpoint of a line is given below as,

Where the coordinates of points W and Z are,

Substituting (x, y) coordinates to find the midpoint, X of line WZ,

Recall, Y is the midpoint of XZ,
Where the coordinates of points X and Z are,

Substituting (x, y) coordinates to find the midpoint, Y of line XZ,

The coordinates of point Y are (3, -1).