x 12” board. that gives you four 40” boards. save the 15” boards you have left.
next, draw a 11 1/4 inch line on the 15” boards.
cut along that line and save the scraps for the shelves later on.
next, draw a diagonal line from one corner to the opposite corner on the 11 1/2” x 11 1/2” boards.
cut along that line to make four triangles from the two boards.
from the right angle of each triangle, measure two inches and make a four inch line. then measure 2 7/8 inches and make a four inch line. connect the upper ends of the four inch lines.
cut out the lines using a jig saw 