4. It takes Xiaohua 9 minutes to go from the first floor to the fourth floor, so how many minutes does it take him to go from the first floor to the ninth floor?
4．小华从一楼到四楼要用9分钟，那么，他从一楼到九楼要用多少分钟？
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

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

<gadget id="calculator">3 * 8</gadget>
<output>24</output>

<result>24</result>