A batch of the same steel pipes piled up has a trapezoidal cross-section, with 12 on the top layer, and each upper layer is one less than the lower layer, a total of 6 layers. How many steel pipes are there in total?
一批同样的钢管堆成的横截面是梯形，最上层是12根，每上层比下层少1根，共6层．这堆钢管共有多少根？
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">12 + 5</gadget>
<output>17</output>

<gadget id="calculator">12 + 17</gadget>
<output>29</output>

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

<gadget id="calculator">29 * 3</gadget>
<output>87</output>

<result>87</result>