On a map with a scale of 1:5,000,000, the distance between Xi'an and Ankang is 4.5 cm. One day Mr. Li drove back to Xi'an from Ankang at a speed of 90 kilometers per hour. How many hours would it take him to get from Ankang to Xi'an?
在比例尺是1：5000000的地图上，量得西安到安康之间的距离是4.5厘米．一天李老师自驾车从安康回西安，车速是每小时90千米，他从安康到西安需要几个小时？
<gadget id="calculator">1 / 5_000_000</gadget>
<output>1/5_000_000 = around 0</output>

<gadget id="calculator">4.5 / (1/5_000_000) / 100_000 / 90</gadget>
<output>2.5</output>

<result>2.5</result>