grain store sold 21 tons of rice last week, which was 1/6 more than flour. How many tons of flour did the grain store sell last week?
某粮店上一周卖出大米21吨，比面粉多(1/6)，粮店上周卖出面粉多少吨？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 + (1/6)</gadget>
<output>7/6 = around 1.166667</output>

<gadget id="calculator">21 / (7/6)</gadget>
<output>18</output>

<result>18</result>