Question 648591
We have 12+7+11+9+15 M&Ms. This is 54 M&Ms. This is our sample space: S. Let E be the event that you pick a green or orange M&M. There are 12+9 Green or Orange M&Ms. That means 21 satisfy this event.  Then  P[green or orange m&m] = N(E)/N(S) =  21/54 where N(E) is just the number of elements in that set: 21. 

I know that was formal so let me break it down.

You have 54 M&Ms to choose from. 21 are green or orange. When you reach in the bag, you have a 21/54 chance of picking a green or an orange.