Hey Pavan

Let me just brief you up on this. You will need to build a good profile to get into IIM Shillong. For this you need a good composite score in which a student with  greater than 60% marks in graduation will receive full marks, and candidates with 80% or above marks in both 10th and 12th will receive full marks. Hence you need to score above 80% in your 10th and 12th at the least and above 60% in graduation.