10.
Total cost = $51
Remove cost for parking
$51 - 6 = $ 45 (this price includes the cost of general admission tickets and riding passes)
$3.50 + $5.50 = $9
$ 45/ $9 = 5
There were 5 people in the family.
11.
Let the number be 'n'
5n - 18 - 4n = -36
n = -36 + 18 = -18
The number is -18