First off, the music sheet is not used here. You're right it's all in the showcase. From the showcase, you take the 4th place in performance & the 2nd place in composition. These two places add to be 6. Which is used, and shown on the music box(on the circle with the + sign). This is the only dial(circle with an icon) given to you. But, that's where the 4 and 2 come into play. You put the dials(the music note and the trophy) at 4 & 2. Then after you are just doing the equation given with these two numbers.
E.g:
Since 4+2=6
What is 4x2=?
Or 4-2=?
Or 4/2=?
Please let me know if this was more helpful! If not, I can try again to re-explain it. :)