在select和textbox中的值之间相乘

Question

你好我希望得到一些帮助，请选择一个值和一个文本框中的值。结果是自动给出的，但不正确。

<script>
function calculate() {
    var myBox1 = document.getElementById('departement1').value; 
    var myBox2 = document.getElementById('transaction1').value;
    myBox1 = parseFloat(myBox1);
    myBox2 = parseFloat(myBox2);
    var result = document.getElementById('result'); 
    var myResult = myBox1 * myBox2;
    result.value = myResult;
}
</script>

<tr>
    <td>                         
        <label>Price</label>
    </td> 
    <td> 
        <select name="departement1" id="departement1" oninput="calculate()">

        </select>
    </td>
</tr>  
<tr>
    <td> 
        <label># of transactions</label> 
    </td> 
    <td> 
        <input type="text" name="transaction1" id="transaction1"   
                size="30" oninput="calculate()" />
    </td>
</tr> 
<tr>
    <td> 
        <label>Pre-tax salary</label> 
    </td> 
    <td> 
        <input id="result" />
    </td>
</tr>