Explanation:
Meter reading at the beginning of the month (Falgun) = 2400
Meter reading at the end of the month (Chaitra) = 2425
Electricity consumed during the month = Meter reading at the end of the month - Meter reading at the beginning of the month
Electricity consumed during the month = 2425 - 2400 = 25 units
Now,
20*3=Rs60
5*7=Rs35
Service charge is Rs 50
So,
the total amount =60+35+50
=Rs145