Your friend has $100 when he goes to the fair. he spends $10 to enter the fair and $20 on food. rides at the fair cost $2.00 per ride. which function can be used to determine and how much money he has left over after x rides?
a. f(x) = -2x + 70
b. f(x) = 2x + 70
c. f(x) = -2x - 70
d. f(x) = -30x + $100

The answer is A f(x)=-2x + 70
The $100 budget, $10 entrance fee, as well as the $20 spent on food are considered to be constants with the budget being a positive and the money spent on the entrance and food as negatives. This provides you with a positive 70. The variable x here is the number of rides your friend might take and the -2 multiplied to it is the money to be spent per ride. 

Example:
When your friend has ridden a total of 5 rides, x = 5 therefore 

-2(5) + 70 = 60

Your friend upon going on 5 rides would have $60 left.