A pile of logs is piled up in a trapezoidal shape. There are 4 logs on the top layer and 7 logs on the bottom layer. There are 4 layers in total. How many logs are there in this pile?
将一堆原木堆成梯形，最上一层有4根，最下一层有7根，一共堆了4层，这堆圆木有多少根．
<gadget id="calculator">4 + 7</gadget>
<output>11</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">11 * 2</gadget>
<output>22</output>

<result>22</result>