There are 9 steel pipes in the top layer and 20 steel pipes in the bottom layer. From top to bottom, there are 1 more steel pipes in each layer. There are 12 layers in total. How many steel pipes are there in this pile?
一堆钢管，最上层9根，最下层20根，从上到下每层多1根，共12层，这堆钢管一共有多少根？
<gadget id="calculator">9 + 20</gadget>
<output>29</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">29 * 6</gadget>
<output>174</output>

<result>174</result>