Let Sale be 3,00,000 , Variable cost be 240,000 Contribution will be 60,000( sale - Vcost)
Now BES be 40% of Actual sale that comes to 1,20,000 and cont come to 24,000 ( sale * P/v ratio)
MOS will be 60 % of Actual sale that comes to 180,000 and cont comes to 36,000( sale * p/v ratio)
and fixed cost in MOS is always 0 and rest of all is profit that is 36,000.
and Profit/MOS = 36000/180,000
=20% which is equal to P/v Ratio.
It's easy just make a table and follow the formula you will come to know okey .
All the Best