There are 18 steel pipes in the bottom layer and 12 steel pipes in the top layer. There are 7 layers in total. How many steel pipes are there in this pile?
一堆钢管，最下层有18根，最上层有12根，一共放了7层．这堆钢管有多少根？
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">30 * (7/2)</gadget>
<output>105</output>

<result>105</result>