Expense Mangement App- Auto addition and subtraction + adding new textboxes

Me and my friend have been attempting to develop and app with one of the features including auto addition. So there's a textbox,user puts in a number,another box appears,they put in a other number,another appears and somewhere on the bottom left of the screen the total will be appearing. They also need to be able to add and subtract said values. These boxes for numbers will be on the right and on the left they can write whatever it is they're doing that uses these expenses. They'll set a budget for the day on top and once they go over it they will hear a couple beeps + the screen will flash red.Basically an expense management app. Any ideas on how we can do this?? We've been working on this for weeks but gotten nowhere. We're pretty new here.

Why don’t you share any Screenshots or at least blocks which you have worked for weeks,

So it will easier to address your issue

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