Objects _y value depending on mouse pos and stage height

Example 1
If the _y position of the mouse is 0, the stage height is 100 and the object height is 200, then the position of the object would be _y= 0;

Example 2
If the _y position of the mouse is 50, the stage height is 100 and the object height is 200, then the position of the object would be _y= 100;

Example 3
If the _y position of the mouse is 100, the stage height is 100 and the object height is 200, then the position of the object would be _y= -100;

The equation for the above is:
_y.object = (object_height%stage_width-_ymouse)-2;

The problem is the above equation dosen't work for different stage heights and object heights.

Anyone know of a universal equation?

Thanks