Room B2 "Aperture"

Of the two doors, make sure you know which is the exit.

You'll need to open the other one first.

That should be a simple matter of arranging the arrows.

Once the inner door is open, you can set about opening the main door.

Think about where the particle can reach with the first arrow arrangement. What changes would you need to make to get it to the receiver?

Consider what arrows are available and which ones you can move.

The arrows don't necessarily need to stay still whilst the particle is moving.

Make sure you move the right-arrow on the right of the room out of the way.

Move the left-arrow after the particle has passed over it - move it to the bottom-right corner of the room.