the tocal cost of the electric bill from Sep1 to Oct is $8167.5
Step-by-step explanation
Step 1
find the consumption of the month by obtaining the difference of the registered data
from Sept 1 to Oct 1

Step 2
now to know the total cost of the electric bill for that month, we need to use the expression

then, let

replace

therefore, the tocal cost of the electric bill from Sep1 to Oct is $8167.5
Step 3
Now, do the same for the other monts

June Electric bill: $11925

November electric bill: $7042.5
I hope this helps you