In order to take admission in IIT Bombay you should have 75% marks in your boards exams or you should be in top 20 percentile.

For SC/ST you should have 65% marks.

You can also refer below link to know in detail

JEE Advanced eligibility Criteria

IIT Bombay takes admission through JEE Advanced.

In order to appear for JEE Advanced you have to qualify for JEE Main exam first.  

Good Luck!!