A person bought a chicken for 80 yuan, sold it for 90 yuan, then he thought it was not worth it, bought it back for 100 yuan, and sold it to another person for 110 yuan. How much did he earn?
一个人花80块钱买了一只鸡，90块钱卖掉了，然后他觉得不划算，花100块钱又买回来了，110块卖给另外一个人．问他赚了多少？
<gadget id="calculator">80 + 100</gadget>
<output>180</output>

<gadget id="calculator">90 - 180</gadget>
<output>-90</output>

<gadget id="calculator">110 + (-90)</gadget>
<output>20</output>

<result>20</result>