Solid Bug Ghost's Shell

Mission
Collect 15 shells of Soil Ghost Bugs

Reward
Experience 5420100

Form
Available 3 times

NPC
Donwhang Baekako

Monster
Soil Ghost Bugs/ Earth Ghost Bugs

Scenario
A while ago there was an incident where workers working at stone caves at Donwhang were attacked by bugs with hard shells, causing chaos. His workers fought back, but the bugs' shells were too hard, causing the equipment to break instead.
I sought revenge with my comrades, but the hard shells and sharp nails were too much to handle, and we had to return without doing much damage.
So would you be able to collect just 15 of these bugs' shells?
Amongst these shells you collect, there will be some broken ones. These are useless to me, so sell those at the shops.