There is a section of slope. A car travels 30 kilometers per hour when going uphill and 45 kilometers per hour when going downhill. It takes 4 hours to go back and forth. How many kilometers is the length of this road?
有一段坡路，一辆汽车在上坡时每小时行30千米，下坡时每小时行45千米，往返一次需4小时，这段路长多少千米？
<gadget id="calculator">4 * 45</gadget>
<output>180</output>

<gadget id="calculator">30 + 45</gadget>
<output>75</output>

<gadget id="calculator">180 / 75</gadget>
<output>12/5 = around 2.4</output>

<gadget id="calculator">30 * (12/5)</gadget>
<output>72</output>

<result>72</result>