To get admission in BSC chemistry (H)  best of three is considered not 4 . and it's mandatory to include physics and chemistry in best 3 so your third subject can be CS . Which makes your percentage app. 95%. 

Hi there,
Hope you are doing well.
Since in the best four only the four subjects with highest marks scored are considered, your best four subjects would be:- Chemistry, Physics, Computer Science and Maths.
Your best four total would be:- 96+95+95+92= 378

Your best four percentage would be 378/4= 94.5%.

Hope it would help.
Thank You