Scratch

Hello friends,
My name is Anna and I need your help please.
I need a Scratch program that can calculate water charges.
I would really appreciate you help.

Here is wat i need.

The first 10000 litres or less if applicable is charged at €0.001 per litre BUT THIS CHARGE IS SUBTRACTED FROM THE FINAL AMOUNT AND IS CALLED THE DOMESTIC WAIVER.

The next 10000 litres (10001 to 20000) is charged at €0.002 per litre.

There is a standing charge of €20.00 per billing period for water meter rental.

Design and write a program that will input the present and previous meter readings and will then calculate the quantity of water used, the charges in each range and add the meter rental, subtract the domestic waiver amount applicable and finally calculate the amount due by the householder.

Well thats it I hope somebody can help thank you.