sporting goods store sold 12 pairs of badminton rackets of a certain brand in one morning, with a total income of 540 yuan. If you sell 21 pairs of badminton rackets of the same brand in the afternoon, how much should you earn?
某体育用品商店一天上午卖出某种品牌的羽毛球拍12副，共收入540元．下午卖出同牌的羽毛球拍21副，应收入多少元？
<gadget id="calculator">540 / 12</gadget>
<output>45</output>

<gadget id="calculator">45 * 21</gadget>
<output>945</output>

<result>945</result>