150 people from a certain school go to a place 32 kilometers away for a spring outing. There is only one car that can carry 50 people. It is known that the walking speed of the students is 4 kilometers per hour, and the speed of the car when carrying people is 40 kilometers per hour. , the speed of the empty car is 50 kilometers per hour. In order to make all the students arrive at the destination as soon as possible, how many hours will it take to combine walking and driving?
某校150人到32千米外的某地春游，只有一辆能载50人的这汽车，已知学生步行的速度是每小时4千米，汽车载人时的速度为每小时40千米，空车的速度为每小时50千米，为了使全体学生尽快到达目的地，采用步行和做车相结合的方法，至少需要多少小时？
<gadget id="calculator">6.4 / 4</gadget>
<output>1.6</output>

<gadget id="calculator">5.12 / 4</gadget>
<output>1.28</output>

<gadget id="calculator">1.6 + 1.28</gadget>
<output>2.88</output>

<result>2.88</result>