JSFiddle - React, Tailwind, and code Playground

HTML

<form name="rechner">

	<label>Zeile Input Felder 1: </label>
	E <input type="number" id="e_1" oninput="Rechner1()"/>
	A <input type="number" id="a_1" oninput="Rechner2()"/>
	<hr/>
	<label>Zeile Input Felder 2: </label>
	E <input type="number" id="e_2" oninput="Rechner1()"/>
	A <input type="number" id="a_2" oninput="Rechner2()"/>
	<hr/>
	<label>Zeile Input Felder 3: </label>
	E <input type="number" id="e_3" oninput="Rechner1()"/>
	A <input type="number" id="a_3" oninput="Rechner2()"/>
	<hr/>
	<label>Zeile Input Felder 4: </label>
	E <input type="number" id="e_4" oninput="Rechner1()"/>
	A <input type="number" id="a_4" oninput="Rechner2()"/>
	<hr/>
<label>Ergebnis: </label><input type="number" id="ausgabe" oninput="Rechner1()">
<hr/>
<label>Neu: </label><input type="number" id="neu" oninput="Rechner1()"/>
<hr/>
<label>Ergebnis Neu: </label><input type="number" id="ausgabe2" oninput="Rechner1()">
</form>

JavaScript

function Rechner1() {
	for (let i=1; i<=4; i++) {
		schreibeWert("a", i,Math.round(leseWert("e", i) * 12));
	}

	berechneSumme();
}

function Rechner2() {
	for (let i=1; i<=4; i++) {
		schreibeWert("e", i, Math.round(leseWert("a", i) / 12));
	}	

	berechneSumme();
}



function berechneSumme() {
	let summe = 0;
	for (let i=1; i<=4; i++) {
	summe = summe + leseWert("a", i);     // Frage: Runden?!
	}

	document.rechner["ausgabe"].value = summe;	
	
	document.rechner["ausgabe2"].value = summe+document.rechner["neu"].valueAsNumber || 0;
}


function leseWert(typ, nr) {
	return document.rechner[typ + "_" + nr].valueAsNumber || 0;
}

function schreibeWert(typ, nr, wert) {
	document.rechner[typ + "_" + nr].value = wert;
}