Pleae see attched spreadsheeet, I have made a simple UI so far for estimating cost based on a combobox options mutiplied by textbox input, it works so far, pretty much cost per unit area mutiplied by gross floor area inputted by the user. However, now i would like to provide more options, such that whenever the user select an item (various type of ward renovation), a pre-defined list of sub-items (options) appear on listbox 1 (inlcluded) and 2 (not included), and the user can add or remove them and their cost (H17-20) be deducted or subtracted from the total cost (after multuplication by area). I have tried starting this step at the top of the list but i am stuck, as I am not familiar with even the basic language, but the UI works with the first step combobox and multiplication. Any help would be appreicated, thank you very much