To solve this, you must define the variable first.
You can usually choose the variable to be what we are asked to find.
Let the number of people in the family be x.
The amount paid by each person (x) for admission and ride passes was $3.50+$5.50=$9.00
Only one payment for parking ($6) was made by the family.
The total amount spent was $9×x+$6
The total amount spent was $51.
Therefore, 5 people in the family went to the fair.
