The landscaping team plans to plant 1,200 trees this year, and 780 have already been planted. The rest will be completed in 3.5 days. How many trees are planted per day on average?
园林绿化队今年计划植树1200棵，已经植了780棵，剩下的用3.5天完成，平均每天植树多少棵？
<gadget id="calculator">1_200 - 780</gadget>
<output>420</output>

<gadget id="calculator">420 / 3.5</gadget>
<output>120</output>

<result>120</result>