what is the trick for multilevel [eg 3 levels] of affiliate

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what is the trick for multilevel [eg 3 levels] of affiliate earnings [php5] ?
500usd booking
through "A" affiliate where register via "B" and B via "C"
A gets 10%*500
B gets 5%*500
C gets 3%*500 (first this become affiliate and do others)

Am I approximate correct in %s ?

I must do an affiliate table with among others the names(AIDs) of the 3 ?
What if a booking done throgh B not A ? or through A, and not B or C ? what will be the %s ?