In Xiaoyue's piggy bank, there are 18 more 50-cent coins than 1-cent coins, and the total value of 5-cent coins is 21 yuan more than the total value of 1-cent coins. How many coins are there in the piggy bank?
小悦的存钱罐里，5角硬币比1角硬币多18枚，5角硬币的总值比1角硬币的总值多21元．存钱罐里共有多少枚硬币？
<gadget id="calculator">0.5 * 18</gadget>
<output>9</output>

<gadget id="calculator">21 - 9</gadget>
<output>12</output>

<gadget id="calculator">0.5 - 0.1</gadget>
<output>0.4</output>

<gadget id="calculator">12 / 0.4</gadget>
<output>30</output>

<gadget id="calculator">30 + 18 + 30</gadget>
<output>78</output>

<result>78</result>