값 넘겨주기 input 이렇게 쓰는게 맞을까요?

        <tr>
            <th scope="row"><label for="wr_5">정가/할인율<strong class="sound_only">필수</strong></label></th>
            <td><input type="text" name="wr_5" class="box" value="<?php echo $wr_5 ?>" id="wr_5" required class="frm_input required" size="20" maxlength="20"> x
   <input type="text" name="wr_6" class="box" value="<?php echo $wr_6 ?>" id="wr_6" required class="frm_input required" size="10" maxlength="20"> %</td>
        </tr>

<script>
$(".box").onkeypress(function(){
var result=$("input[name='wr_5']").val()+$("input[name='wr_6']").val();
 $("input[name='wr_7'].val(result);//
});
</script>

        <tr>
            <th scope="row"><label for="wr_7">할인가<strong class="sound_only">필수</strong></label></th>
            <td><input type="text" name="wr_7" value="<?php echo $wr_7 ?>" id="wr_7" class="box" required class="frm_input required" size="10" maxlength="20"></td>
        </tr>​

5 번 6 번 값을 더해서 7번에 바로 보여주기 하고 싶은데요. 저렇게 해봤는데 안되서요.