Answer
See below
Work Step by Step
$A\cup B=${Dirk,Johan,Frans,Sarie,Tina,Klaas,Henrika}
$n(A\cup B)=7$
$n(A)=$4
$n(B)=$5
$A\cap B=${Frans,Sarie}
$n(A\cap B)=2$
$n(A)+n(B)-n(A\cap B)=4+5-2=7$
$n(A)+n(B)-n(A\cap B)=7=n(A\cup B)$
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