Hello Shwetakshi,

The formula for percentage calculation is-

(Total obtained marks / maximum marks of the exam ) ×100

Here excluding your 6th subject marks you have a percentage of 70%. 

And exchanging  maths with your 6th subject your percentage comes to 79% 

Now, which of your subjects will be taken for the calculation of percentage for your admission depends upon the course you are applying and the university you are applying in. 

For eg- in Delhi University, admission in Bsc Chemistry requires the percentage of only 3 subjects ( physics and chemistry mandatory). 

I would suggest you go through the university you wish to apply in and then check how many subjects they take to calculate percentage for admission and then check the subjects they say are mandatory. 

I hope you best for your result. You can reply to the question here if you still have doubt.