Hi! The chain on my mother's mountain bike fell off the large gear and slipped inbetween the frame and the gears. Actually, it's stuck, and I can't get it out! What i need to do is remove the gears so I can free the chain.

Already I have used those 6-sided screw tool to remove a bolt. But still the crank arm and gears do not come off? What do I need to do to remove the gears? Note-the bike does not pedal because the chain is stuck.

Attached are photos of the stuck chain, the gears, and the bolt. Please help me save this bike!

P.S. Don't bother to tell me to take it to a shop. I'm into learning and collecting tools.