For llb, DU conducts an entrance exam called DU LLB entrance. Its admission is not based on class 12th marks but on the rank secured in that exam. In 2018 cutoff for general category students in the fouth round was 99 in terms of rank and 226 in terms of marks. So you should take up the entrance exam and score at least 226 for du llb admission. In 2017, the required marks were 249. So it is tangible every year. Better try for more than 250 to be on safer side.