This challenge takes place in Course 3 Chamber 3. You will use 3 Portals in the first room and 2 Portals in the second room.
Portal 1 - Go to the edge of the platform you start on, look straight and slightly down. Fire a Red Portal (There are 3 tiles, aim for the middle one).
Portal 2 - From where you are, turn 90 degrees left and you should see a wall where the Hard Light surface ends, fire your Yellow portal at this wall (You might have to get a better angle).
From here, you should be able to walk across the surface, through the portal and get to the switch (Go to it). Have your partner walk across the surface, but not go through the portal until they catch the safety cube (You can hit the button as many times as you want).
Portal 3 - Once your partner has the safety cube and is through the portal, walk on where the Hard-Light Surface is coming/spawning from (There is a small part of metal you can walk on).
From there, look up and to the right and you should just barely be able to see the wall above you. Fire your red portal there, and you should then be able to walk through your yellow portal to where the cube needs to be placed.
Portal 1 - Once you enter the room, go to the right corner on the platform you are currently on (As far right and as close to the water as you can) and look up . Fire the red portal in the space/line between the 2nd and 3rd tile (From the right).
Portal 2 - Fire the yellow portal at the wall where the Hard Light Surface ends.
If you've done it right, you should be able to launch yourself with the catapult and deflect yourself onto the platform (Make sure you move yourself toward the platform after you deflect)..