There are two strips of paper with a length of 30 mm each, and the length of the pasted together is 56 mm. What is the length of the part pasted together?
有两条各长30毫米的纸条，粘贴在一起长56毫米，粘贴在一起的部分长多少毫米．
<gadget id="calculator">30 - 56</gadget>
<output>-26</output>

<gadget id="calculator">30 + (-26)</gadget>
<output>4</output>

<result>4</result>