Jiayou Supermarket can sell 630 kilograms of pears a week, and Convenience Supermarket can sell 420 kilograms of pears in 7 days. On average, how many kilograms more pears does Jiayou Supermarket sell per day than Convenience Supermarket?
家友超市一周能销售630千克梨，便民超市7天能销售420千克梨，家友超市平均每天比便民超市多销售多少千克梨？
<gadget id="calculator">630 / 7</gadget>
<output>90</output>

<gadget id="calculator">420 / 7</gadget>
<output>60</output>

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

<result>30</result>