I've been trying to figure this out for hours! If you are only able to do one of the parts (a,b, or c), I am mostly stuck on letter b!

I've been trying to figure this out for hours! If you are only able to do one of the parts (a,b, or c), I am mostly stuck on letter b! Ignore what I wrote next to the problem (b); Im not sure if its correct or even relevant. Thank you so much!