PLSPLS 數學呀.....QuickQuick

1.)May went to the Ocean Park by bus with her mother,
father,brothe r and sister.
TheagesofMay,
her brother and her sister are 11,7and9 respectively.
They paid a total of $21 for the bus ride.
If all children under12pay half-fare of an adult.(列出完整既式)
21x2+(21/2)*3
=42+31.5
=$73.5

Let the fare of an adult be $n;
Fare of father (adult) = n
Fare of mother (adult) = n
Fare of May (child-halffare) = 0.5n
Fare of May,s brother (child-halffare) = 0.5n
Fare of May,s sister (child-halffare) = 0.5n
Thus,
Father + mother + may + brother + sister = 21
That is,
n + n + 0.5n + 0.5n + 0.5n = 21
3.5n = 21
n = 6
Ans.
Fare of father (adult) is $6;
Fare of mother (adult) is $6;
Fare of May (child-halffare) is $3;
Fare of May,s brother (child-halffare) is $3;
Fare of May,s sister (child-halffare) is $3.