Hlw sir..This is neha😋I have doubt in this chapter that how can we k

This question was asked in Ex 14.1, 3

Hlw sir..
This is neha😋
I have doubt in this chapter that how can we know that where class mark and class size are to be used
Plzz tell this ..... I really don't understand
I am confused.
Even my boards are coming 7th march