There are a total of 15 2-cent and 5-cent coins with a total value of 51 cents. How many more 2 cent coins are there than 5 cent coins?
2分和5分硬币共15个，币值共51分．2分硬币比5分硬币多多少枚．
<gadget id="calculator">5 * 15</gadget>
<output>75</output>

<gadget id="calculator">75 - 51</gadget>
<output>24</output>

<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">24 / 3</gadget>
<output>8</output>

<gadget id="calculator">15 - 8</gadget>
<output>7</output>

<gadget id="calculator">8 - 7</gadget>
<output>1</output>

<result>1</result>