Answer
$\{1980, 1990, 2000, 2010\}$
Work Step by Step
Let's call:
$A$ - The set of years in which more than $55\%$ were pretty happy.
$B$ - The set of years in which $12\%$ were not too happy.
$C$ - The set of years in which more than $55\%$ were pretty happy or $12\%$ were not too happy.
$C=A\cup B$
From the graph we can see that:
$A=\{1990, 2000, 2010\}$
$B=\{1980\}$
$C=A\cup B=\{1980, 1990, 2000, 2010\}$
