There are some apples, 50 kg in each box, and 389 kg are left after packing 9 boxes. What is the total weight of these apples?
有一些苹果，每箱装50千克，装了9箱后还剩389千克，这些苹果一共重多少千克．
<gadget id="calculator">50 * 9</gadget>
<output>450</output>

<gadget id="calculator">450 + 389</gadget>
<output>839</output>

<result>839</result>