The elder brother goes upstairs twice as fast as the younger brother. It takes 3 minutes for the younger brother to go from the first floor to the third floor. How many minutes does it take for the older brother to go from the first floor to the ninth floor?
哥哥上楼的速度比弟弟快1倍，弟弟从一楼到三楼要3分钟，哥哥从一楼到九楼需要多少分钟．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">3 / 2 / 2</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">(3/4) * 8</gadget>
<output>6</output>

<result>6</result>