JSFiddle - React, Tailwind, and code Playground

HTML

<p>              
<input type="text" name="txttipo" id="Tipo2" value="0"  onChange="multiplicar();" readonly>
</p>
 
<label>Tipo de Cuota:</label>
<select id="Tipo" name="tipo" onChange="multiplicar();">
<option value="1" >Mensual</option>
<option value="2">Anual</option>
<option value="3">Semestral</option>
</select>

JavaScript

var tipo2  = document.getElementById("Tipo").value; 
document.getElementById("Tipo2").value = tipo2;