Cacher is the code snippet organizer for pro developers

https://www.youtube.com/channel/UCdSu9Y0xAyY8V77vj6mQ-0g/videos

link/ether: b8:27:eb:ba:7a:1b
brd: ff:ff:ff:ff:ff:ff
inet: 169.254.249.234/16
brd: 169.254.255.255

Create your CHD folder in here:
/opt/retropie/configs/mame-advmame/image

So yours would be
/opt/retropie/configs/mame-advmame/image/area51/area51.chd