World 4 - Level 3
Move the reflector along the yellow path, and destroy the box marked with a yellow "X". Before the cannon fires again, remove the those two reflectors (green) and build a bridge at the green "X". In order to get the Bonus Points you'll want to move the blue wood box to safer position, such as the blue "X".
Open the purple door - time your entrance carefully with the Flying Saucer. You will have to "dance" around the Reflector and eventually move it one space up and one space left... this will cause the Flying Saucer to follow the white path and get out of your way. Now use the remaining two Reflectors to destroy one box along the right path and build a bridge at the white "X". Collect all Rainbow Coins, and use the two wooden boxes to reach the Bonus Coins.