On Sunday, Xiao Ming rode a bicycle from Xuantian Lake to Bayue Mountain at 50 meters per minute. It took 90 minutes, and it took 30 minutes to go down the mountain when he returned. How many meters per minute does Xiao Ming travel on average?
星期天，小明骑车从玄天湖到巴岳山每分钟行50米，用了90分钟，返回时下山用了30分钟，小明往返平均每分钟行多少米？
<gadget id="calculator">50 * 90 * 2</gadget>
<output>9_000</output>

<gadget id="calculator">90 + 30</gadget>
<output>120</output>

<gadget id="calculator">9_000 / 120</gadget>
<output>75</output>

<result>75</result>