There are a total of 20 5-cent coins and 2-cent coins, and the total value of the coins is 0.7 yuan. How many 2-cent coins are there?
有5分硬币和2分硬币共20枚，币值一共是0.7元，其中2分硬币有多少枚
<gadget id="calculator">0.7 * 100</gadget>
<output>70</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">70 - 40</gadget>
<output>30</output>

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

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">20 - 10</gadget>
<output>10</output>

<result>10</result>