After the 1-up mushroom at the top of the screen there is a zig zag brick lay out with red and green koopas. Let green ones go by then duck and smash the first four bricks on the lowest level. Next, trap a red koopa on the far left by smashing the second brick. Smash the fourth brick and jump and stand on the brick left between the two spaces you made. Carefully jump on the trapped koppa.