The rice bought in the cafeteria is three times that of the flour, 10 kg of rice is used up every day, and 4 kg of flour is used up every day. A few days later, the flour was used up and there were 30 kilograms of rice left. How many kilograms of flour did the cafeteria buy?
食堂买来的大米是面粉的3倍，大米每天用去10千克，面粉每天用去4千克．若干天后，面粉用完了，大米还剩30千克．食堂买来面粉多少千克？
<gadget id="calculator">30 / 10</gadget>
<output>3</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/10) - (1/4)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">3 / (1/20)</gadget>
<output>60</output>

<result>60</result>