Which situation is most likely to have a constant rate of change

The answer is:

B. The cost for a group of friends to see a movie compared to the number of friends.

We can tell that this is most likely to have a constant rate of change because of what we already know about movie prices.

Movie prices are fixed, therefore, no matter how many friends you bring, the total price will always go up by the same amount.

For example:

Let's say a movie ticket costs $5 and you brought 3 friends with you. Since there are 4 people in total, you'd have to pay $20 for the tickets (5x4=20). Just as you're about to pay, Sally shows up. Now you have to pay for 5 people in total. How much do you need to pay now?

You will now need to pay $25 (5x5=25) for all of the tickets. Even though you now have 5 people in the group, you still only have to pay $5 for each ticket.

This is an example of a constant rate of change.