Its going to be 4. This is because you would first look at how many balloons have been blown up and the total you start out with. After noticing these items, you would multiply these two together, since its a fraction, so 12*(1/3). this will give you 4. now you would add your outcome and your total together(5+4) getting 9, and subtract your total from your previous total (9-12), getting your answer of 4 remaining.
