Leading to First Playable

The game starts with a bubble with one number on one side of the seesaw
(seesaw should still be horizontal)
The floating bubbles contain expressions including a '+' or '-' sign in
between (e.g. "3-1" or "2+2")
You are able to drag one of these floating bubbles into place on the
empty side
Once this bubble is in place, the two bubbles 'pop' and leave the number
in place