Hey, I just wanted to video a week or so ago about asking a girl for her number. You might want to check that out for more in-depth tips. Since you guys have a connection through playing instruments that's a perfect conversation starter. You can ask her if she's played at any concerts or in any performances or if she just generally enjoys playing music on her own. There's a lot of ways you can take the conversation and after you talk to her for a while, throw in asking for her number as a general part of the conversation by saying "Hey let me get your number so we can hang out sometime and maybe go to a concert."