vegetable field is trapezoidal, the upper base is 4 meters, the lower base is twice as long as the upper base, and the height is 3 meters. If cabbage is planted at an average of 20 square decimeters per plant, how many cabbages can be planted in this vegetable field?
一块菜地为梯形，上底4米，下底是上底的2倍，高3米．如果按照平均每株20平方分米种白菜，这块菜地大约可以种多少株白菜？
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / 2 / (1/5)</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">12 * (15/2)</gadget>
<output>90</output>

<result>90</result>