First Function & eval()

function testQuestion(question) {
var answer = eval(question);
var output = "What is " + question + "?";

var correct = '<IMG SRC="correct.gif">';
var incorrec = '<IMG SRC="incorrec.gif">';

var response = prompt(output, "0");

return (response == answer) ? correct : incorrec;
}

</SCRIPT>

<BODY>

var result = testQuestion("10 + 10");

document.write(result);

</SCRIPT>