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.
