If it takes 3 minutes to saw a large tree into two pieces, how many minutes will it take to saw it into 8 pieces?
把一根大树锯成两段要用3分钟，如果锯成8段需要多少分钟．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<result>21</result>