From this mark, draw a line that is perpendicular to the top run. Extend the line to the back edge of the 2"x12" board.

Next, draw a notch that is 1 1/2" by 3 1/2". This will be used to attach a 2"x4" board.

Now, all of the drawing on the board should be complete. Use a circular to cut out the stair stringer. Only cut up to the end of the line, not past it. Due to the curve of the circular saw blade, some material will remain in the corners. Use either a hand saw or a jig saw to remove the remaining material.