Answer
58.5 million
Work Step by Step
$n(A)=58.0$ (in millions)
$n(B)=0.6$
$n(A\cap B)=0.1$
The question is $n(A\cup B)$
$n(A\cup B)=n(A)+n(B)-n(A\cap B)=58.0+0.6-0.1=58.5$
$58.5$ million sites contained either "tea party" or "coffee party" or both.