The reason that this is A is because 5$ is the initial fee and you dont pay any more than that, since 21$ is the max you can afford it is going to be less than or equal to 21. and if it is 2.75$ per stop then it is the number of stops times 2.75. A is your answer.
edit: and the 50 kilometers doesnt have any value in the situation so basically it was just there to confuse you or throw you off.
Step-by-step explanation: It never talks about 50 so i don't know why that is there so I think it is A because 21 dollars is more than 5+2.75, (not 100% sure but at least 85% sure)
