Hello

I am a newb. I have made a few programs, calculator, flag displayer etc

I am really stuck on a program i am required to create,


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Design and create a program to be used by an interior decorator to estimate the cost of painting a room. The decorator needs to enter the following input data:
• the height of the room (between 2 and 6 metres),
• the length of all 4 walls (between 1 and 25 metres).
The program should calculate the total area of the room to be painted (4 walls only, without the ceiling). The program should allow a choice of three paints:
• luxury quality, which costs £1.75 per square metre
• standard quality, which costs £1.00 per square metre
• economy quality, which costs £0.45 per square met
The decorator should also be able to choose to use undercoat paint if required, which costs £0.50 per square metre.
The program should display an itemised bill with a total.

As part of the design, you need to include the following:
 data design
 algorithm
 user interface design
 design of test plan



I dont know where to start, could someone help me please, i have tried making the program but now i am in desperate need of help.

Thank you