Display Updated Price from a set list of prices after listbox options are changed

Creating a program on visual studio for a meal ordering service where user gets list of meals and list of meal sizes. There is a set price for each meal with each size, e.g. Full English Child = 3.40, Full English Adult = 5.00. I need the price of order label to update instantly when the selections are changed in the list box. If they change either of list box selections then price should update. Running totals will not work as price list is already provided.

Below is a screenshot of my form.

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I am using switch case with the list box and then the radio buttons embedded into each switch statement