Answer: The refrigerator cost in this month is $4.5 approximately.
Step-by-step explanation:
Since we have given that
Amount of watt of electric power = 320 W
Number of days = 30
Unit cost of electricity = $0.13/Kwh
Hold factor = 
Number of hours in a month = 24
So, the refrigerator cost in this month would be

Hence, the refrigerator cost in this month is $4.5 approximately.
3.14 on the length. but if you add to a graph send another one to my comment and show me
explanation
1: (pi)5^2 = 78.54 then multiply that by 11 and you get 863.94
2: (pi)13^2= 530.93 then multiply that by 8 and you get 47247.44
3. (pi)18^2= 1017.88 then multiply that by 22 and you get 22393.36
I could be wrong but 20.5 and 7.5
Answer:
You shoud invest $0.204, it is an small amount each month.
The formula to calculate the monthly saving is

with PP: periodic payments, A: amount desired, n: number of payments in one year, Y: number of years.
In this case A = 88, n= 12 (the payments are monthly), Y=18, APR=7%.
Replacing in the formula you obtain that 