A pile of logs is piled up into a trapezoid, with 7 logs on the top layer and 12 logs on the bottom layer. There are 6 layers from top to bottom. How many logs are there in total?
一堆圆木堆成梯形，最上层7根，最下层12根，从上往下有6层，共有多少根圆木．
<gadget id="calculator">7 + 12</gadget>
<output>19</output>

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

<gadget id="calculator">19 * 3</gadget>
<output>57</output>

<result>57</result>