Answer
$\{1990, 2000\}$
Work Step by Step
$A=\{x|x$ was a year in which more than $30\%$ were very happy$\}$
$B=\{x|x$ was a year in which fewer than $12\%$ were not too happy$\}$
$A\cap B=?$
From the graph we can see that:
$A=\{1980, 1990, 2000\}$
$B=\{1990, 2000\}$
$A\cap B=\{1990, 2000\}$
