A convoy transported a batch of disaster relief goods. It was originally planned to travel 50 kilometers per hour and reach the disaster area in 4.5 hours. The actual travel was 75 kilometers per hour. Based on this calculation, how many hours will it take to complete the journey? (solution with arithmetic and ratio)
某车队运送一批救灾货物，原计划每小时行50千米，4.5小时到达灾区，实际每小时行75千米，照这样计算，行完全程需要多少小时？(用算术和比例解)
<gadget id="calculator">4.5 / 75</gadget>
<output>0.06</output>

<gadget id="calculator">50 * 0.06</gadget>
<output>3</output>

<result>3</result>