Principal Zhao has to drive 450 kilometers to the provincial capital to attend the meeting. In the morning, he drove 180 kilometers in 2 hours. At this speed, how many hours will he have to drive to get to the meeting place?
赵校长要开车到450千米的省城去参加会议，上午他2小时开了180千米，按照这样的速度，他还要开几小时才能到会议地点？
<gadget id="calculator">180 / 2</gadget>
<output>90</output>

<gadget id="calculator">450 / 90</gadget>
<output>5</output>

<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<result>3</result>