Adults go upstairs twice as fast as children. It takes 3 minutes for children to go from the first floor to the third floor, and how many minutes it takes for adults to go from the first floor to the fifth floor.
大人上楼速度比小孩快一倍，小孩从一楼到三楼要3分钟，大人从一楼到五楼要几多少分钟．
<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">5 - 1</gadget>
<output>4</output>

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

<result>3</result>