1. The problem states that a piece of blueberry pie costs 4. 2. A piece of apple pie costs 50% more than a piece of blueberry pie. 3. To find the cost of a piece of apple pie, calculate 50% of 4 and add it to 4. 4. Calculate 50% of 4: $$0.50 \times 4 = 2$$ 5. Add this amount to the original cost of blueberry pie: $$4 + 2 = 6$$ 6. Therefore, a piece of apple pie costs 6.