In a trapezoidal field, the upper base is 30m, the lower base is 20m shorter, and the height is 40m. A total of 200 trees are planted. How many square meters does each tree occupy on average?
一块梯形地，上底是30m，比下底短20m，高是40m，一共种200棵树，平均每棵树占地多少平方米？
<gadget id="calculator">30 + 30 + 20</gadget>
<output>80</output>

<gadget id="calculator">40 / 2 / 200</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">80 * (1/10)</gadget>
<output>8</output>

<result>8</result>