Xiaomi went to climb the mountain. It took 45 minutes to go up the mountain, and 30 minutes to go down the mountain by the same route. The uphill walk was 9 meters less per minute than the downhill. Find the downhill speed.
小米去爬山，上山花了45分钟，原路下山花了30分钟，上山每分钟比下山每分钟少走9米，求下山速度．
<gadget id="calculator">45 * 9</gadget>
<output>405</output>

<gadget id="calculator">45 - 30</gadget>
<output>15</output>

<gadget id="calculator">405 / 15</gadget>
<output>27</output>

<result>27</result>