The percentage of Americans who are retired has been increasing over the last decade. This is causing some concern because health care, social security, and other costs will be the responsibility of a smaller group of people. That is, as the percentage of retired people increases, the percentage of working age people decreases. The following model predicts the percentage of retired people based on demographic data¹:

 $\displaystyle {R}=\frac{{t}}{{873.36}}-{2.15}$ 

where R is the percentage (as a decimal) of Americans who are retired in the year t (for example, the year 1995 would be t = 1995). Use this model to complete the table below by solving for the year. State your answers to the nearest tenth of a percent and to the nearest year.

Year	% of Retired People
1970	%
1980	%
1990	%
	10%
	15%
	20%

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