The chicken farm raised 1028 chickens this year. If it raises another 172 chickens, it will be exactly three times the number of chickens raised last year. How many chickens were raised last year?
养鸡场今年养鸡1028只，如果再养172只，正好是去年养鸡只数的3倍，去年养鸡多少只？
<gadget id="calculator">172 + 1_028</gadget>
<output>1_200</output>

<gadget id="calculator">1_200 / 3</gadget>
<output>400</output>

<result>400</result>