calculate.js

    function calcula(op) {
      const operations = {
        '+': (a, b) => a + b,
        '-': (a, b) => a - b,
        '*': (a, b) => a * b,
        '/': (a, b) => a / b,
      }
      
      const operation = operations[op]

      const n1 = document.getElementById("n1").value;

      const n2 = document.getElementById("n2").value;
      document.getElementById('ex13').value = operation(n1, n2)
    }