According to one mathematical model, the average life expenctancy for American men born in 1900 was 55 years. Life expectancy has increased by about 0.2 year for each birth year after 1900. If this trend continues, for which birth year will the average life expentancy be 73 years?

a) Write an equation to model the problem. Let $t$ represent the number of years after 1900 and let $n$ represent men's life expectancy at that time. For example $t = 12$ and $n=57.4$ in the year 1912.
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b) Solve the equation, then answer the question given above. (Note: You are asked for a year, not a value for $t$.
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