A pig pendant is 4.5 yuan, Xiao Ming bought 3 pieces, and he gave the salesperson 20 yuan, how much should he get back?
一个小猪挂件4.5元，小明买了3个，他给售货员20元，应找回多少元．
<gadget id="calculator">4.5 * 3</gadget>
<output>13.5</output>

<gadget id="calculator">20 - 13.5</gadget>
<output>6.5</output>

<result>6.5</result>