JSFiddle - React, Tailwind, and code Playground

HTML

<td></td>
<td align="center"><input type="text" id="tonaj_1" name="tonaj_1" style="width:100px; border:1px solid #000; text-align:right;" /></td>
<td align="center"><input type="text" id="kilometri_1" name="kilometri_1" style="width:100px; border:1px solid #000; text-align:right;" /></td>
<td align="right"><input type="text" id="norma_1" name="norma_1" style="width:75px; border:1px solid #000; text-align:right;" /></td>
<td align="right"><input type="text" id="litri_1" name="litri_1" style="width:75px; border:1px solid #000; text-align:right;" /></td>
<td align="right"><input type="text" id="zaredeno_gorivo_1" name="zaredeno_gorivo_1" style="width:85px; border:1px solid #000; text-align:right;" /></td>
<td></td>
<td align="center"><input type="checkbox" id="po_vlekach_1" name="po_vlekach_1" style="border:1px solid #000;" /></td>

JavaScript

var tonaj_1 = $("#tonaj_1").val();
		var kilometri_1 = $("#kilometri_1").val();
		if ($('po_vlekach_1').is("checked"))
		{
			var norma_1 = parseFloat(tonaj_1)*35/100 + 20;
		}
		else 
		{
			var norma_1 = parseFloat(tonaj_1)*35/100 + 25;
		}
		$("input[name=norma_1]").val(norma_1);
		var litri_1 = parseFloat(kilometri_1) * parseFloat(norma_1)/100;
		$("input[name=litri_1]").val(litri_1);