In order to measure the height of a big tree, Xiao Ming's measurement results are: the height of the ruler is 12 decimeters, and its shadow length is 2.5 decimeters; the measured shadow length of the big tree is 3 meters. Please help Xiao Ming calculate the height of the big tree.
小明为了测量一棵大树的高度，他测量的结果是：标尺高度12分米，它的影长是2.5分米；测得大树的影长是3米．请你帮小明算一算大树的高度．
<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">36 / 2.5</gadget>
<output>14.4</output>

<result>14.4</result>