At a guess, rate/kW/month is the cost the energy supplier charges (in INR?) per kW of supply capacity, per month you have that supplied.
So since your friend has an 8.79kW supply, and the rate cost is 75 INR per kW per month, they pay a monthly cost of 659.25 INR. But, they are billed only every 60 days, so you pay approximately twice that (they approximate the year as having 366 days) but once every 60 days. That's what the (a*b*c*12)/366 is working out.
It looks like the rate per kW increases with higher supply, probably because it costs incrementally more to supply a bigger supply line, and it's more likely (especially in India) that will be used continuously for things like air conditioning which requires higher downstream rating costing the power company more money.