It took Doudou 30 seconds to walk from the first floor to the third floor. At this speed, how many seconds does it take him to walk from the first floor to the sixth floor?
豆豆从一楼走到三楼用了30秒，照这样的速度，他从一楼走到六楼需要多少秒．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">15 * 5</gadget>
<output>75</output>

<result>75</result>