If a number is added to 210 and then subtracted from 70, the result is 320. What is the number?
一个数加上210再减去70，结果是320，这个数是多少．
<gadget id="calculator">70 - 210</gadget>
<output>-140</output>

<gadget id="calculator">320 + (-140)</gadget>
<output>180</output>

<result>180</result>