A pile of trapezoidal logs has 7 logs on the top layer and 13 logs on the bottom layer. How many logs are there in this pile?
一堆梯形圆木，顶层7根，底层13根，这堆圆木共有多少根．
<gadget id="calculator">7 + 13</gadget>
<output>20</output>

<gadget id="calculator">13 - 7</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

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

<gadget id="calculator">20 * (7/2)</gadget>
<output>70</output>

<result>70</result>