For  out of 100

Maths = 85=> 85/2 = 42.5

Phy = 88 => 88/4 => 22

Chemistry = 83 => 83/4 = 20.75

Total = 85.25

you got 85.25 cut off mark for 100

85.25/100

To calculate for 200

Maths = 85 => 85

Physics = 88=> 88/2 = 44

Chemistry = 83=> 83/2 = 41.5

Total = 85+44+41.5 = 170.5

you got 170.5/200

I Hope I have cleared your question.

If you have doubts,  please feel free to ask here in comment section.

Thank you.