Hello Aspirant,Hope you are doing well

In general you can do LLB after B.Com as L.L.B is a post graduation course and the eligibility criterion to do L.L.B is graduation. Hence B.COM is the graduation. The duration will be of 3 yrs. The eligibility criteria for LLB course is that one should have B.A/ B.Sc/ B.Com degree with minimum 40% marks in aggregate for general category and 35% in aggregate for SC/ST students.

As you are stating that you have passed the exam with below 40% ,so it makes you to ineligible for the admission.If you are keen to get the admission into LL.B you can try in private colleges .

Hope this helps you

ALL THE BEST