There is a big tree and a small tree, the height of the small tree is equal to (1/4) the height of the big tree. After a period of time, the height of the two trees has increased by 30 cm, and the height of the small tree is equivalent to (2/7) of the height of the large tree. How much taller is the original big tree than the original small tree?
有一棵大树和一棵小树，小树的高度相当于大树高度的(1/4)．经过一段时间，这两棵树的高度都增加了30厘米，这时小树的高度相当于大树高度的(2/7)．原来的这棵大树比原来的这棵小树高多少厘米？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(2/7) * 30</gadget>
<output>60/7 = around 8.571429</output>

<gadget id="calculator">30 - (60/7)</gadget>
<output>150/7 = around 21.428571</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/7) - (1/4)</gadget>
<output>1/28 = around 0.035714</output>

<gadget id="calculator">(150/7) / (1/28)</gadget>
<output>600</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">600 * (3/4)</gadget>
<output>450</output>

<result>450</result>