Jokes and Laughs...

she's sitting in your lap

The rolling ball has a hole in it, and must be lighter...therefore, the balance won't be changed, or, not enough to spike C.
Also, the platform the full ball is laying on, is not horizontal, so, as soon as enough weight comes on the other scale....the ball will roll to the right.....and STILL spike c....?

l think the answers are correct. I guess gravity and speed gives the ball enough force to make the seesaw move down and spike C. I guess the little triangle is supposed to slow down the ball so all the power stays in that end and makes it go down. 
And because a ball is round it will move a little (to the left) when the seesaw goes up (maybe because it is hit from the right?). I guess it will follow the sloping line of the wall and thus hit B. I don't know if it makes any sense but in my head it does