55, now I get to rant about Duet to people on the internet, while I think it sounds amazing (tho it's not my favourite) there's one thing I can't get over, it's said that Mari spent a lot of time practicing to play it perfectly (side note, don't do that), but her part wasn't actually hard, don't get me wrong you would need som practice with the piano to play it, but it's pretty simple, the only bits that would require some more practice (but not that much more) is the begining when you have to move your hand across most of the keyboard and there's a place in the middle when you have to play chords with both hands, there's also a bastard moment at the beginning but I would call it just bad sheet music (you have to play a very spread out "chord" (G#4 C5 C6) with one hand- I actually can't do it because my hand isn't big enough and I have pretty big hands, but i would just play one of the notes with the other hand that's not doing anything at that moment anyway). But for someone that in any way is practicing playing the piano it's really simple and easy stuff. I actually think that Sunny's violin part is way harder than Mari's piano since there's a lot of long notes that are hard to do on a violin. Mari was so obsessed with getting the piece just right, but the harder part was Sunny's.

TLDR: In Duet the violin part is harder than the piano part