A duck and 2 chickens weigh 10 kg in total, and each chicken weighs 3 kg. What is the weight of the duck in kilograms?
一只鸭和2只鸡共重10千克，鸡每只重3千克，鸭重多少千克千克．
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<result>4</result>