Answer
a. $2039$, $37\%$.
b. Approximately, they're the same in the graph.
Work Step by Step
$\{-3x+10y=160$
$\{x+2y=142$,
a. $10y=160+3x$,
$y=\frac{160+3x}{10}$,
$y=16+\frac{3x}{10}$,
$y=\frac{142-x}{2}$,
$y=71-\frac{x}{2}$,
$71-\frac{x}{2}=16+\frac{3x}{10}$,
$71-16=\frac{3x}{10} + \frac{x}{2}$,
$55=\frac{8x}{10}$,
$\frac{550}{8}=x$,
$x=68.75$
$x=69^{th} year$,
when $x=69^{th} year$ after $1970$, $y=36.6$. $y=37\%$ for each group.
Year $1970+69=2039$
b. Approximately, they're the same in the graph.
