How do i add the .toUpperCase() its not working ?

var correct = 0;
var questions = 3;
var questionsLeft = '[ ' + questions + ' questions Left ]';
questions -= 1;
var correctGuess = false;
var answerOne = "Yellow";
var questionOne = prompt("What color is the sun?" + questionsLeft);
if ((questionOne.toUpperCase())=== answerOne) {
  document.write('<p> the answer' + answerOne + 'is correct </p>');
correct += 1;
} else {
document.write("<p> Sorry! you are incorrect</p>");
}
questionsLeft = '[' + questions + ' questions Left ]';
questions -= 1;
var answerTwo = "Blue";
var questionTwo = prompt('What colour is the sky' + questionsLeft);
if ((questionTwo.toUpperCase()) === answerTwo) {
document.write('<p> Well done! the answer' + answerTwo + 'is correct </p>');
correct +=1;
} else {
document.write ("<p> Sorry you are incorrect </p>");
}
questionsLeft = '[' + questions + ' questions Left ]';
questions -= 1;
var answerThree = "Green";
var questionThree = prompt('What colour is the grass' + questionsLeft);
if ((questionThree.toUpperCase()) === answerThree) {
document.write('<p> Well done! the answer' + answerThree + 'is correct </p>');
correct +=1;
} else {
document.write ("<p> Sorry you are incorrect </p>");
}
document.write ("<p> You got" + correct +" out of 3 questions.</p>");
if ( correct === 3 ) {
  document.write('<p> Well Done! you earned a Gold crown </p>');
}
if ( correct === 2 ) {
  document.write('<p> Well Done! you earned a Silver crown </p>');
}
  if (correct === 1) {
    document.write('<p> Well Done! you earned a Bronze crown </p>');
}