If a stack of lumber is 6 feet high and piece of lumber is 3 inches thick, how many pieces of lumber are in the stack?

Step 1 ：Convert the height of the stack from feet to inches. Since 1 foot is equal to 12 inches, a 6 feet high stack is \(6 \times 12 = 72\) inches high.

Step 2 ：Divide the total height of the stack by the thickness of each piece to find out how many pieces are in the stack. So, \(\frac{72}{3} = 24\).

Step 3 ：Final Answer: There are \(\boxed{24}\) pieces of lumber in the stack.