it's a pity that i have to find the answer from different site n post it here for everyone's benefit. i do not wat hapenned for goiit. I EARLIER POSTED THE SAME QUESTION, but didn't get the correct answer so i asked it as a expert question here, but no ans here too...........
so iam answering my own question now..........
2NaHco3 ------------- > Naco3 + co2+ H2O
168 gms ------------> 44 co2 ( for loss in weight, CO2 gas must be taken into account)
x gms -------------> 66 gms of co2
x = 252 gms of NaHco3 by solving
=> 252 x 100/80 (as the mixture contains 80% of NaHco3 ) = 315 gms....
=> 360 - 315 = 45 gm of Naco3
please correct if it wrong.......