Grandpa’s family has a vineyard. Last year, they harvested a total of 3,900 kilograms of grapes, an increase of 30% over the previous year. How many kilograms of grapes were harvested in the previous year?
爷爷家有个葡萄园，去年共收葡萄3900千克，比前年增产了三成，前年收葡萄多少千克．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 + (3/10)</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">3_900 / (13/10)</gadget>
<output>3_000</output>

<result>3_000</result>