Hello Vinayak

We cannot calculate the marks on the basis of percentile. You could calculate your probable marks using the response sheet and the question paper which was released by the NTA. All of the correct responses to the questions asked in the JEE Main examination was present in the answer key.

Question paper and the corresponding responses could be checked from the official website from January 14 to 17(05:00 PM).

Also, it is difficult to tell you about the qualifying marks as JEE Main exam is being conducted twice by NTA for the first time. With 85 percentile , you might qualify the exam but nothing can be said exactly until the result of the April exam.

Good Luck!