Here's the ballast the Division A licensed drivers(top 15 of last season and red roof licensed drivers) must carry in order to take part in division B races. It represents 2,5% of the total weight of the car(without fuel or driver).

Round 1(XRG): 29 kg
Round 2(XFG): 24 kg
Round 3(FXO): 28 kg
Round 4(RAC): 20 kg
Round 5(UF1): 15 kg
Round 6(RB4): 30 kg

Failure to carry the correct amount of ballast will result of a disqualification of the session.

So rookies (White roofers) dont need to add weight?

Quote from Bmxtwins :

So rookies (White roofers) dont need to add weight?

No. Only red(and upper) licensed drivers and the top 15 of the last season's drivers championship have to carry that ballast.