There is a girl here with a bike and no money. The shifter for the front derailleur is broken. The cable for the rear derailleur is broken. The chain was continually rubbing on the front derailleur, and made a noise. She asked her friend to find a rock she could put between the front derailleur and seat tube, to hold the derailleur in position, and stop the noise. When I saw this, I adjusted the limit screws in both the front and rear derailleurs. It now works fine as a single speed, and did not cost any money.

The bike would be a lot better with a new cable for the rear derailleur. I may or may not buy a new cable for her in the future.