Lägga ihop värden från dropdowns och skriva ut en text

<?php

if (isset($_POST['submit'])) {
    $value1 = $_POST['val_1'];
    $text1 = $_POST['option_text'];
    $value2 = $_POST['val_2'];
    $text2 = $_POST['option_text_2'];

    $sum = $value1.$value2;
    $sum = intval($sum);

    switch ($sum) {
        case $sum:
            echo "$text1 och $text2";
            break;
    }
}

?>

<form method="post">
    <select name="val_1" onchange="setTextField(this)" required>
        <option value="" selected disabled>Välj</option>
        <option value="1">mjölk</option>
        <option value="2">kaffe</option>
        <option value="3">äpple</option>
    </select>
    <input type="hidden" id="option_text" name="option_text" value="">
    <select name="val_2" onchange="setTextField2(this)" required>
        <option value="" selected disabled>Välj</option>
        <option value="1">havregryn</option>
        <option value="2">kakao</option>
        <option value="3">mjöl</option>
    </select>
    <input type="hidden" id="option_text_2" name="option_text_2" value="">
    <button type="submit" name="submit">Skicka</button>
</form>
<script>
    function setTextField(ddl) {
        document.getElementById('option_text').value = ddl.options[ddl.selectedIndex].text;
    }
    function setTextField2(ddl) {
        document.getElementById('option_text_2').value = ddl.options[ddl.selectedIndex].text;
    }
</script>