According to statistics, the precipitation in Hanchuan City in March this year reached 90 mm, an increase of about 20% compared with the same period last year. How many mm was the precipitation in Hanchuan City in March last year?
据统计，汉川市今年三月份降水量达90mm，比去年同期约增加二成，汉川市去年三月份降水量约多少mm．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">90 / (6/5)</gadget>
<output>75</output>

<result>75</result>