Lan Lan's home is 150 meters away from the school. It takes 9 minutes to go to school, and only 6 minutes to get home after school. Lan Lan's average speed is how many meters per minute.
兰兰家离学校150米，上学用9分钟，放学只用6分钟就回到了家，兰兰上学放学的平均速度是每分钟多少米．
<gadget id="calculator">9 + 6</gadget>
<output>15</output>

<gadget id="calculator">2 / 15</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">150 * (2/15)</gadget>
<output>20</output>

<result>20</result>