Got a few questions which hopefully someone can clarify

1. If I take a QR flight which is booked through QR but credit to BA does QR pay BA to deposit miles into my account? What does BA make from giving me the miles when I haven't paid them anything?

2. If I book a reward seat on QR through BA miles what do BA pay to QR for this? Is it a set amount of a fare or do they in return get seats to sell on BA flights?