JSFiddle - React, Tailwind, and code Playground

HTML

<p>Сумма: <span id="info1">30</span></p>

<select  id="money">
  <option value="10">Rub</option>
  <option value="20">Usd</option>
  <option value="30">Eur</option>
</select>

<p>Валюта: <span id="info2"></span></p>

JavaScript

function costCalculator() {
    
var y = document.getElementById("money").value; 
info1.innerHTML = y
        
//var x = document.getElementById("money").value;   
var z = document.querySelector(`option[value="${y}"]`).innerText;
console.log(z);
info2.innerHTML = z;

}

money.onchange=costCalculator;