Last year, the per capita annual income of rural residents in western my country was about 4,200 yuan, an increase of 20% over the previous year. How much was the per capita annual income of rural residents in western China?
去年，我国西部农村居民人均年收入约为4200元，比前年增加了20%，前年西部农村居民人均年收入约为多少元？
<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">4_200 / (6/5)</gadget>
<output>3_500</output>

<result>3_500</result>