Do you tryed some thing so far?
Did you created a project with a form?
In this form , do you added the labels, and the corresponding text boxes to enter the data needed?
Also, do you added a response label and textbox? And a button to start the calculation?
Did you added an event to the button click to know when the user wants to do the calculation?
In this event, do you validate the correcness of the input data?
Do you wrote the formula calculations?
And, Do you put the result in the result text box?