JSFiddle - React, Tailwind, and code Playground

HTML

<select class="qtd-parc" type="text" name="qtd-parc" />
    <option value="1" selected>1</option>
			<option value="2">2</option>
			<option value="3">3</option>
			<option value="4">4</option>
			<option value="5">5</option>
			<option value="6">6</option>
			<option value="7">7</option>
			<option value="8">8</option>
			<option value="9">9</option>
			<option value="10">10</option>
			<option value="11">11</option>
			<option value="12">12</option>
			<option value="13">13</option>
			<option value="14">14</option>
			<option value="15">15</option>
			<option value="16">16</option>
			<option value="17">17</option>
			<option value="18">18</option>
			<option value="19">19</option>
			<option value="20">20</option>
			<option value="21">21</option>
			<option value="22">22</option>
			<option value="23">23</option>
			<option value="24">24</option>
			<option value="25">25</option>
			<option value="26">26</option>
			<option value="27">27</option>
			<option value="28">28</option>
			<option value="29">29</option>
			<option value="30">30</option>
			<option value="31">31</option>
			<option value="32">32</option>
			<option value="33">33</option>
			<option value="34">34</option>
			<option value="35">35</option>
			<option value="36">36</option>
			<option value="37">37</option>
			<option value="38">38</option>
			<option value="39">39</option>
			<option value="40">40</option>
			<option value="41">41</option>
			<option value="42">42</option>
			<option value="43">43</option>
			<option value="44">44</option>
			<option value="45">45</option>
			<option value="46">46</option>
			<option value="47">47</option>
			<option value="48">48</option>
			<option value="49">49</option>
			<option value="50">50</option>
<input class="valr-parc" type="text" name="valr-parc" placeholder="0,00" />
<input class="total-parc" type="text" name="total-parc" readonly />

JavaScript

$(document).ready(function(){
		var qtd_parc   = $(".qtd-parc");
    var valr_parc  = $(".valr-parc");
    var total_parc = $(".total-parc");
    var dif  = $(".diferenca");
    var avista     = $(".avista"); 
    var zerar = $(".zerar");
    
	valr_parc.on("keyup", function(){
    	$(this).val($(this).val().replace(/\D/g,'').replace(/[0-9]{12}/, "").replace(/(\d{1})(\d{1,2})$/, "$1,$2").replace(/(\d)(?=(\d{3})+(?!\d))/g, '$1.').replace(/^(\d)/g,"R$ $1")); 
		var nw_valr_parc = valr_parc.val().replace(/[^\d.,]/g, '').replace(".", "").replace(".", "").replace(".", "");
		var multiplica = qtd_parc.val() * nw_valr_parc.replace(",", ".");
			total_parc.val(multiplica.toFixed(2).replace(/\D/g,'').replace(/(\d{1})(\d{1,2})$/, "$1,$2").replace(/(\d)(?=(\d{3})+(?!\d))/g, '$1.').replace(/^(\d)/g,"R$ $1"));
	
    });
    
	qtd_parc.on("change", function(){
    	$(this).val($(this).val().replace(/[^\d]/g, '')); 
		var nw_valr_parc = valr_parc.val().replace(/[^\d.,]/g, '').replace(".", "").replace(".", "").replace(".", "");
		var multiplica = qtd_parc.val() * nw_valr_parc.replace(",", ".");
			total_parc.val(multiplica.toFixed(2).replace(/\D/g,'').replace(/(\d{1})(\d{1,2})$/, "$1,$2").replace(/(\d)(?=(\d{3})+(?!\d))/g, '$1.').replace(/^(\d)/g,"R$ $1"));
    });
});