Each Leyangyang pendant is 4.5 yuan, Dongdong bought 3, he paid the salesperson 20 yuan, how much should he get back.
每个乐羊羊挂件4.5元，冬冬买了3个，他付给售货员20元钱，应该找回多少元．
<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>