Zhang Xin's family planted 70 sunflowers and harvested 21 kilograms of sunflower seeds. Li Peng's family planted 60 sunflowers and harvested 15 kilograms of sunflower seeds. Which family of sunflowers harvested more per tree on average? How much?
张新家种了70棵向同葵，收了21千克葵花籽，李鹏家种了60棵向同葵，收了15千克葵花籽，哪家种的向日葵平均每棵收获多些？多多少？
<gadget id="calculator">21 / 70</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 / 60</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/10) - (1/4)</gadget>
<output>1/20 = around 0.05</output>

<result>1/20 = around 0.05</result>