A pile of the same steel pipes, 9 on the top and 21 on the bottom, 13 layers in total, how many steel pipes are there in this pile
一堆同样的钢管，最上层9根，最下层21根，共13层，这堆钢管共有多少根
<gadget id="calculator">9 + 21</gadget>
<output>30</output>

<gadget id="calculator">13 / 2</gadget>
<output>13/2 = around 6.5</output>

<gadget id="calculator">30 * (13/2)</gadget>
<output>195</output>

<result>195</result>