The K790 train from Nanchang to Xi'an travels an average of 90 kilometers per hour, and it takes 21 hours to reach Xi'an. How many kilometers is the railway from Nanchang to Xi'an?
从南昌到西安的K790次列车平均每小时行90千米，途经21小时才能到达西安，南昌到西安的铁路长多少千米．
<gadget id="calculator">90 * 21</gadget>
<output>1_890</output>

<result>1_890</result>