The school cafeteria bought a batch of rice, used 45kg every day, and after 18 days, there was still 90kg. How many kilograms is this batch of rice?
学校食堂买回一批大米，每天用45kg，用了18天后还有90kg．这批大米共多少千克？
<gadget id="calculator">45 * 18</gadget>
<output>810</output>

<gadget id="calculator">810 + 90</gadget>
<output>900</output>

<result>900</result>