The height of the school teaching building is 12 meters, and the shadow length is 18 meters. If the shadow length of a big tree measured at the same time is 21 meters, how tall is the tree?
学校教学楼的高度是12米，影长是18米．如果同一时间量得一棵大树的影长是21米，这棵树有多高？
<gadget id="calculator">12 / 18</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(2/3) * 21</gadget>
<output>14</output>

<result>14</result>