Use 60 yuan to buy 2 yuan stamps and 5 yuan stamps, a total of 18 pieces. How many 2 yuan stamps are there?
用60元钱买2元的邮票和5元的邮票共18张．其中2元的邮票有多少张．
<gadget id="calculator">5 * 18</gadget>
<output>90</output>

<gadget id="calculator">90 - 60</gadget>
<output>30</output>

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

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

<result>10</result>