car drives from place A to place B. After driving for 15 hours, the car exceeds the midpoint of the two places by 30 kilometers, and the distance from place B is still 840 kilometers. How many miles per hour does the car travel on average?
一辆汽车从甲地开往乙地，行了15小时后，汽车超过两地中点30千米，这时距离乙地还有840千米．这辆汽车平均每小时行多少千米？
<gadget id="calculator">840 + 30</gadget>
<output>870</output>

<gadget id="calculator">870 + 30</gadget>
<output>900</output>

<gadget id="calculator">900 / 15</gadget>
<output>60</output>

<result>60</result>