Programming CheckBoxes in Visual Basic Studio 2010

I want to add a charge as "shipping fee" on the total price of the customer if he checks the shipping checkbox So how can write its code in a simple way ?

To rephrase the problem:(more clarification) if customer checks the shipping checkbox, 5% of the total price will be added to the bill automatically.

and this the whole question I stuck with: (my problem with g point)

Create a Visual Basic project to calculate the total price of purchased product. a. Enter the quantity of product. b. Enter unit price of product. (cost of one product) c. Calculate the price of product by multiplying quantity and unit price. (as price amount) d. If the price amount is greater than or equal to 5000 then discount will be 5% of price amount of product. e. If the price amount is greater than or equal to 3000 and less than 5000 then discount will be 3.5% of price amount of product. f. If the price amount is less than 3000 then discount will be 2.5% of price amount of product. g. Use a checkbox that has text Shipping. If you click check box then Extra shipping charge as 5 % of Price amount should be added to the total price, otherwise shipping charge as 0 should be added to the total price. h. Calculate total price by using the formula given below. Total price = price amount – discount +shipping. i. Display Total Price. j. Check for any invalid input data and display a message to the user for invalid data.