Answer: three pieces.
The piece of wood is 6/8 inches long - this fraction can be simplified to 3/4 by dividing both the numerator and denominator by 2.
Thus, he cuts a piece of wood that is 3/4 inches long into 1/4 inch pieces.
1 goes into 3 three times, so the piece of wood can be cut into three 1/4-inch pieces.