Lele has 10 yuan. If she wants to buy two books worth 7 yuan, how much is the difference?
乐乐有10元钱，要买两本7元钱的书，还差多少元钱．
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">14 - 10</gadget>
<output>4</output>

<result>4</result>