A person bought a chicken for 8 yuan, and sold it for 9 yuan. Then he thought it was not worth it, so he bought it back for 10 yuan, and then sold it to another person for 11 yuan. How much did he earn from this chicken?
一个人用8元钱买了一只鸡，9元钱卖掉了，然后他觉得不划算，有用10元钱买回来了，再以11元钱卖给另外一个人．这只鸡他赚了多少元．
<gadget id="calculator">8 + 10</gadget>
<output>18</output>

<gadget id="calculator">9 - 18</gadget>
<output>-9</output>

<gadget id="calculator">11 + (-9)</gadget>
<output>2</output>

<result>2</result>