First of all you would have to multiply both 6 and 2/3 by 3, resulting in a new equation, 18/1 - 2/1. Then, you can proceed to subtract 2 from 18 and you get 16.
If a single board measures 1/12 of a meter then it would take 12 boards to make a meter. Since, the stack is 2 meters high. You would multiply 12 and 2 to get 24. There is 24 boards in the stack.
