how do make if condition for when set combobox and value of this?

My code is n t work!

 <option value="SEL">select</option>
 <option value="10">10</option>
 <option value="11">11</option>
 </select>
            <?php
            if (isset($_REQUEST['selection']) == TRUE) {
                if ($_REQUEST('selection') == 10) {

                    // $vari = $_POST['selection'];
                    //if(!empty(isset($vari))){
                     echo 'hi sarah';

                }

please help me i can t fix it.I am newcomer in php.