There's a 8ft. long board and the carpenter cut off 3 1/2 and 2 1/3.
So first we need to add 3 1/2 and 2 1/3 because the carpenter cut them off the 8ft. long board.
3+2=5 because it's a whole number. 1/2+1/3= 2/6+3/6= 5/6
5 5/6
Now we subtract
8-5 5/6=
7 6/6- 5 5/6= 2 1/6ft.
2 1/6ft. is what remains of the 8ft. board.