trapezoidal orchard has an upper base of 160 meters, a lower base of 120 meters and a height of 30 meters. If each fruit tree covers an area of 10 square meters, how many trees are there in this orchard?
一块梯形的果园，它的上底是160米，下底是120米，高30米．如果每棵果树占地10平方米，这个果园共有树多少棵？
<gadget id="calculator">160 + 120</gadget>
<output>280</output>

<gadget id="calculator">30 / 2 / 10</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">280 * (3/2)</gadget>
<output>420</output>

<result>420</result>