Hi Olga,

It's a bit of work, spent about 20 min on it but it was a combination of offsets, untrims, trims, booleans, separations and a front end labotomy ;)
If you really, really need a step by step explanation (please say no) ;) then I'll need some time.

It's basically what Michael said earlier Here about 'low level' approach.
I was going to give up after 10 min but it got the better of me so I had to finish it.

Cheers