Problem:
A town uses a two-tier system to calculate bill for water usage. For the first 8000 gallons, it is $0.004 per gallon. After the first 8000 gallons, the rate will be $0.007 per gallon. Suppose a customer uses 8500 gallons of water. He will pay $0.004 per gallon for the first 8000 gallons, and $0.007 per gallon for the last 500 gallons. Write a Python program to determine how much a customer needs to pay. Ask the user how much water he has used. Calculate and display the water bill. The following are two examples.
Enter gallons of water used: 2100
Please pay this amount: $8.4
Enter gallons of water used: 8500
Please pay this amount: $35.5