There are 39 coins in a pile of 2 cents and 5 cents, with a total value of 1.5 yuan. How many 5 cent coins are there?
一堆2分和5分硬币共有39枚，共值1.5元．5分的硬币有多少枚．
<gadget id="calculator">1.5 * 100</gadget>
<output>150</output>

<gadget id="calculator">39 * 2</gadget>
<output>78</output>

<gadget id="calculator">150 - 78</gadget>
<output>72</output>

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

<gadget id="calculator">72 / 3</gadget>
<output>24</output>

<result>24</result>