Xiao Ming usually walks 4.5km per hour from home to school, and can arrive at 0.6 hours. Now walking 3km per hour, how long will it take longer than usual to get there?
小明从家到学校，平时每小时走4.5km，0.6时可以到达．现在每时走3km，要比平时多用几时才能到达？
<gadget id="calculator">0.6 / 3</gadget>
<output>0.2</output>

<gadget id="calculator">4.5 * 0.2</gadget>
<output>0.9</output>

<gadget id="calculator">0.9 - 0.6</gadget>
<output>0.3</output>

<result>0.3</result>