How much do you pay teenage babysitter?

[Deminism]

Just wondered what the going rate is? (Full disclosure, we had a 16 yr old do two hours for us after school today, not pick up. Watch tv with two kids and play a few games. Finished 6.30. London. I gave £7.50 and hour so £15).

Sounds fine.
We are in the Midlands.
My dd2 is 18, very experienced, and is First Aid qualified (has 2 x DBS's too if anyone wants them) and can get an arm full of references if anyone wants them. She gets wildly different amounts from different people - from a massively generous wad last NYE, to taking a friend's little one swimming last week for free (just because she loves him).
She always says they can pay whatever they like. There are some that get her a takeaway and a lift home, there are others that pay about a fiver an hour.
Does depend on things like if it is a regular 'sit' / if there is one dc or several / if there is a baby (much more work than say an 8 yr old) / If they have to change nappies / If they have to cook or feed the dc / if they are asleep for most of the time / etc etc