Converting Textbox String - Application That Has 2 Textboxes And A Button

Basically I have an application that has 2 textboxes and a button. What I am trying to do is when the button is clicked, it takes an entered string from box one (which is validated to only accept numbers) adds 235 to it then converts it to hex and finally reverse the string and sets textbox two equal to that value. Note that the final string has to be eight digits so the string may needed to be padded with zeros before the string is reversed. With that said how could I go about doing this? Also I do plan to add 2 more textboxes and another button to undo this process but I am thinking if I can figure out do it one way writing the code to undo the process shouldn't be too hard.