cal.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        function cal(){
            let answer = document.getElementById('answer').value;
            let s = document.getElementById('problem').value;
            let solution=eval(s)
            if(answer==solution){
                alert('정답');
            }
            else{
                alert('틀렸습니다. 정답은 '+solution);
            }
        }
    </script>
</head>
<body>

    <h1>Math Quiz</h1>
    <input type="text" id="problem" value="12*2+20-30"><br>
    <input type="text" id="answer">
    <button onclick="cal()">정답 알아보기</button>
    
</body>
</html>