There are a pile of circular steel pipes with a trapezoidal cross-section. There are 2 pipes in the upper layer and 7 pipes in the lower layer. There are 6 layers in total. How many pipes are there in this pile?
有一堆圆形钢管，它的横截面是梯形，上层有2根，下层有7根，共有6层，这堆钢管共有多少根．
<gadget id="calculator">2 + 7</gadget>
<output>9</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<result>27</result>