Xiaohua bought 5 greeting cards, and Xiaogang bought 3 cards. Each greeting card is 4 yuan, how much less does Xiaogang spend than Xiaohua.
小华买了5张贺卡，小刚买了3张．每张贺卡4元，小刚比小华少用多少元．
<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<result>8</result>