Replacing some numbers in javascript

I have a javascript code that goes into the console of my browser. This code is designed to be used on a maths website that asks questions to you.

Now my script is supposed to be pasted into the browser console, and this script basically removes the = from the "question", puts the "question" into eval() and then inputs the answer into the inputbox.

Here is that code:

Now I get this question here: . Here eval() thinks that it is 16+20 and the answer keeps outputing as 36.

Is there any way to change this to 20-16? I cannot use .replace to change the + into a -, as that will change it for the other + questions as well.

function showAnswer() {
  var inputBox = document.getElementsByClassName("questions-input-adjustment questions-input-width-v3")[0];
  var submitButton = document.getElementsByClassName('question-input-form')[0];

  for (var i = 0; i < 100; i++) {
    var question = document.getElementsByClassName("questions-text-alignment")[0].innerText;
    question = question.replace(' =', '');
    question = question.replace('×', '*')
    question = question.replace('=', '');
    var answer = eval(question);
    inputBox.value = answer;
  }

  var awnser = addbits(equasion)
  var inputBox = document.getElementsByClassName("questions-input-adjustment questions-input-width-v3")[0];
  var submitButton = document.getElementsByClassName('question-input-form')[0];

  for (var i = 0; i < 100; i++) {
    var question = document.getElementsByClassName("questions-text-alignment")[0].innerText;
    question = question.replace(' =', '');
    question = question.replace('×', '*')
    question = question.replace('=', '');

    var answer = eval(question);
    inputBox.value = answer;
  }

  var awnser = addbits(equasion)

  document.getElementById('dashow').innerText = awnser;
  document.getElementsByClassName("questions-input-adjustment questions-input-width-v3")["0"].value = awnser;
}

window.addEventListener("keydown", checkKeyPressed, false);

function checkKeyPressed(e) {
  if (e.keyCode == "81") {
    showAnswer();
  }
}