Working part time, JSA and WTC

A few questions about working part time and benefits.

Is it still possible to earn £20 a week without it affecting JSA payments?

If I earn more than £91(JSA+£20) each week for less than 15 hours, the JSA claim remains open and I still have to sign on every 2 weeks. Is this correct?

Thanks

Edit: Ignore WTC in the title, I was going to ask another question but found the answer.:)