The canteen of the experimental middle school bought 900 kilograms of rice and ate 180 kilograms in 6 days. According to this calculation, how many days can the bought rice last? (Answer with proportional knowledge)
实验中学食堂买来900千克大米，6天吃了180千克．照这样计算，买来的这些大米一共能吃几天？(用比例知识解答)
<gadget id="calculator">180 / 6</gadget>
<output>30</output>

<gadget id="calculator">900 / 30</gadget>
<output>30</output>

<result>30</result>