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Let's define \( t = 0 \) for the year 1960, and increase \( t \) by 5 for each subsequent 5-year interval. Thus, the years translate to:
\[
\begin{array}{c|cccccccc}
\text{Year} & 1960 & 1965 & 1970 & 1975 & 1980 & 1985 & 1990 & 1995 \\
\hline
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