10) Let x be the number of people of this family:
The total paid with the parking is $51
The total paid WITHOUT the parking is $51-$6 = $45
They spent $3.5(x) for the entry, they also spent $5.5(x) for the pass:
3.5(x) + 5.5(x) = 45
9x = 45 and x = 5 people
11) Translate English to Math language:
Let x be this number:
5.x - 18 - 4.x = -36
x - 18 = -36 Add 18 to both sides
x - 18 + 18 = - 36 + 18
x = - 18