Xiao Ming has a total of 10 pieces of 10 yuan and 5 yuan yuan, and the total is 80 yuan, so how many pieces of 5 yuan yuan are there?
小明有10元和5元的人民币共10张，总共80元，则5元的人民币有多少张．
<gadget id="calculator">10 * 10</gadget>
<output>100</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<gadget id="calculator">10 - 5</gadget>
<output>5</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<result>4</result>