Instructions: you will be presented with a context, a question, a arithmetical program about that numerical reasoning. Program is a Numerical Program that will be executed in the Context to generate an Answer. The Context is either Tabular or Textual Data, where the cell values are divided based on a specific delimiter. Read the Context and Program thoroughly and generate only the correct numerical answer from Quesiton. Read the context thoroughly to ensure you know what the passage entails.
Question: what is the variation between the useful lives of the structures and machinery and equipment by the global rolled products segment?
Program: subtract(31, 21)
Context: 
millennium bcp 2011 annual report
1. linearized table evidence: in years the useful lives of structures for global rolled products is 31 ; the useful lives of machinery and equipment for global rolled products is 21 ;
Answer:  Your answer should have exactly 4 paragraphs. Make sure that the last paragraph starts with the word "cautious" and that each paragraph is separated by two new lines.
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