Order priority in a call market ?

I wonder what's the priority during a call market where all orders are executed at once (begining and end of days, or specific low volume stocks).

Some exemples:

• 1 buy order in front of 1 sell order both executed at market price ? What price will be chosen ?
• If last transaction was at $10, and there is 1 buy order at $11 in front of 1 sell order at $8, at what price is the deal closed ? $8, $11, $9.5, $10 ?

Thanks for any answers