A person bought a chicken for 8 yuan, sold it for 9 yuan, and then he thought it was not worth it, so he bought it back for 10 yuan, sold it to another chicken for 11 yuan, and asked how much he earned.
一个人花8块钱买了一只鸡，9块钱卖掉了，然后他觉得不划算，花10块钱又买回来了，11块钱卖给另外一个，问他赚了多少元．
<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>