Add & Subtract Input Values with Javascript

I have a PHP website and added a Javascript code that combines input values then adds them up providing the complete total, then subtract that total amount from a set number and outputs the balance amount. Example: Amount: 1000 Combine Table Amount: 750 Balance: 250 And if user changes any numbers in the fields the table amount and balance changes. The problem I'm having is that I have multiple sections, so from the example above I have 4 of them divided out with different inputs on the same page and the problem is that the 'Amount' portion only takes the amount of the first section and if the amounts are changed or different from the remaining three it only takes the value of the first amount among every other section. So I need a way to individualize each section to read from their own amounts. And currently in values are anchored you have to click on the field for the calculation results to display. I need it able to display with have to click on field.