The calculation data from the input?

For example there are 4 input fields?
How to apply the formula? For example, folded and multiply by another number?

And as in input to enter only numbers?
March 12th 20 at 08:43
1 answer
March 12th 20 at 08:45
> How to apply the formula? For example, folded and multiply by another number?
To Use JavaScript

> And how to input to enter only numbers?
To use JavaScript - hang function to the onkeyup event, which will be cut from the field all except numbers.
You can even specify the type="number" (htmlbook.ru/html/input/type) but, not all browsers supported it seems.

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