It took Xiaoqiang 0.4 hours to go to school at a school 1.8km away from home, and it took 0.2 hours longer for Xiaoqiang to return home from school due to wind and rain.
小强从家出发到离家1.8km远的学校上学花了0.4小时，放学返家路上因刮风下雨比上学时多花了0.2小时，放学时速度比上学时每小时慢多少km？
<gadget id="calculator">1.8 / 0.4</gadget>
<output>4.5</output>

<gadget id="calculator">0.4 + 0.2</gadget>
<output>0.6</output>

<gadget id="calculator">1.8 / 0.6</gadget>
<output>3</output>

<gadget id="calculator">4.5 - 3</gadget>
<output>1.5</output>

<result>1.5</result>