A car travels a certain distance, with an average of 72 kilometers per hour in the first 3 hours, and a total of 309 kilometers in the next 4 hours. How many kilometers per hour does this car travel on average?
一辆汽车行一段路程，前3小时平均每小时行72千米，后4小时共行309千米，这辆汽车平均每小时行多少千米？
<gadget id="calculator">72 * 3</gadget>
<output>216</output>

<gadget id="calculator">216 + 309</gadget>
<output>525</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">525 / 7</gadget>
<output>75</output>

<result>75</result>