var answerInterval = setInterval(function(){
  var answer = document.getElementById('answer');
  if (answer) {
    answer.value = eval(document.getElementById('question').innerHTML
      .replace(' = ', '')
      .replace('x', '*')
      .replace('÷', '/')
    );
    var event = new CustomEvent('keyup', {});
    answer.dispatchEvent(event);
  } else {
    clearInterval(answerInterval);
  }
}, 10);