There are 12 steel pipes with trapezoidal cross-section in the upper layer and 18 steel pipes in the lower layer. There are 6 layers in total. How many steel pipes are there in total?
有一堆堆成横截面是梯形的钢管上层有12根，下层有18根，一共有6层．这堆钢管共有多少根？
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

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

<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<result>90</result>