Help with C# and GUI

Problem: You are a car-rental agency which would like to create a program for their customers to use enabling them to request a car rental quote. You have three levels of cars which rent for the following price/day. Compact = $15, Mid-size = $25, and Luxury = $50. You will need to find how many days they want the rental for. Tax is 7.75%. Some things to consider are that a person needs to be 18 or over to rent a car (check their age). If they are under 25, they are charged an extra $25 a day.

Planning:

Draw a flowchart.