My real life problem is that I am tiling my 12' x 10' room floor which is in the shape of an Irregular Quadrilateral and I want to draw black tile border 4" width and approx. 1 foot away from walls, so far my markings are based on guess work and I am afraid I will end up making a tilted border (as shown in fig 2).
Therefore I would like to know if there is any formula or way to make a properly aligned rectangle inside Irregular Quadrilateral.
As I try to draw in fig 1 (again it is created using guess work) but it was easy in small space like this but for large space I have no idea.
Thank you.