A trapezoidal paddy field has an upper base of 13 meters, a lower base of 17 meters and a height of 4 meters. If the seedlings are transplanted according to an average of 30 square decimeters per hole, how many holes should be inserted?
一块梯形水稻田的上底13米，下底17米，高4米．如果按照平均每穴30平方分米插秧，大约要插多少穴？
<gadget id="calculator">13 + 17</gadget>
<output>30</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">100 / 30</gadget>
<output>10/3 = around 3.333333</output>

<gadget id="calculator">30 * 2 * (10/3)</gadget>
<output>200</output>

<result>200</result>