sir i got 75 marks(obc) ,i want to join iit or nit ,so i have to score how much marks in jee advance and expecting 90% in cbse board 2015.

Private colleges and universities these days are offering huge amounts of scholarships to those scoring 90/80/70 percent marks in +2 and if JEE score is quite good then there may be some other kind of benefits too. you can browse websites of elite institutions for eg. Birla institute if Tech. Patna, Guru Gobind Singh Indraprastha Uni, Delhi, LPU, Phagwara, Shivaji Uni, Kolhapur