I dont know how to calculate academics marks

hey guys im 19M currently in SY and just started to know about CAT and there is no guidance on youtube that how to calculate 10th 12th and grad marks .....can you help me with that ...?

10th 76.17 12th 89.72 and

also want to know that ki grad me only TY (bcom) marks will be considered or all 3 years ...?

in FY i got 6.82 YGPA.....

Also one doubt is that ki someone said me that all subjects of 10th will be considered but in one subject i got grade A (computer) and rest of subjests got marks out of 100s...(photo attetched)