Event 3, Event 2, Event 4, and Event 1.
Explanation:
Event 3 is the least likely to ever happen because neither box A nor B has orange pens making this event least likely. The next is event 2, the chance of choosing a red pen from box for is low because their 7 red pens and 13 green pens so the likely hood of you getting a red pen is low. Event 4 is next, the chance of you getting a green pen from box b is pretty high also considering that there is 6 green pens and 6 red pens it's really a 50/50 making this more likely to happen. and now event 1 this is the most likely to happen because you are choosing randomly from box a meaning there is no desired pen to have so you could get either pen making this event the most likely to happen.
Hope this helped :)