I created a partition to run Snow Leopard on my computer running El Capitan and no longer need it. I allocated 20GB to that partition. Here's what I've done. I first go into Disk Utility, select my partition and click 'Erase'. It apparently erases everything but there is still 67.4 MB being used on the partition that I can't remove:
If I go into finder this is what I see on that partition:
Those are hidden files obviously and I can't delete them. I then go to the hard drive itself and click 'Partition' but when I do that and select the partition I want to remove, the minus button isn't an option:
I can't manually resize the partitions either (I want to re-allocate the disk space to my main drive).
Any ideas on why I can't remove the partition?