This is probably not the first case, but I have tried various methods to recover the lost 50 GB of space from different threads, but neither one of them work. (After removing Boot Camp partition, took a little effort to finally remove all the partitions, but the space used went missing.)
Tried Internet Recovery to go into Disk Utility app didn't work.
Tried using Terminal (not very good at it), so basically copied & pasted some of the commands others have shared, and changed the necessary disk numbers, didn't work for me.
So I figured, might be good that I just post & hopefully someone could give me some advise.
This is what I got: