In a pile of steel pipes, there are 24 steel pipes at the bottom and 6 steel pipes at the top. There is a difference between two adjacent layers. How many steel pipes are there in this pile?
一堆钢管，最底层有24根，最高层有6根，每相邻的两层间相差一根，这堆钢管共有多少根．
<gadget id="calculator">6 + 24</gadget>
<output>30</output>

<gadget id="calculator">24 - 6</gadget>
<output>18</output>

<gadget id="calculator">18 + 1</gadget>
<output>19</output>

<gadget id="calculator">19 / 2</gadget>
<output>19/2 = around 9.5</output>

<gadget id="calculator">30 * (19/2)</gadget>
<output>285</output>

<result>285</result>