Xiaojun walks 4 kilometers per hour from the school to the Children's Palace, and can reach it in 0.9 hours. If you walk 4.5 kilometers per hour, how many hours can you arrive in advance?
小军从学校到少年宫，每小时走4千米，0.9小时可以到达．如果每小时走4.5千米，就可以提前多少小时到达？
<gadget id="calculator">0.9 / 4.5</gadget>
<output>0.2</output>

<gadget id="calculator">4 * 0.2</gadget>
<output>0.8</output>

<gadget id="calculator">0.9 - 0.8</gadget>
<output>0.1</output>

<result>0.1</result>