We cannot find the marks by just knowing the percentile. You first need to understand what a percentile actually means. It is a relative measure based on the performance of all the candidates. It shows that you have performed better from this specific percentage of student.

For example you have scored 80 percentile it means 80 percent of students have scored below you. And let say there were 1000 students  who gave the exam so 80 percentile will indicate that your rank is 200.