Kate and William are getting married. They found a charming venue with a maximum capacity of $50$ people. The venue costs $1000$ dollars, and the caterer charges $50$ dollars for every person who attends the wedding (including the bride and groom).
Besides Kate and William, there are $10$ close family members who will definitely be attending, and they wondered how many additional guests to invite. They decided to graph the relationship between the number of additional guests and the total price per person.

Which axis should represent the price per person?

Potentially, mathematical variables can have any value, but the variables under discussion here are bounded by the real-world context they model.

What is the range of valid values for the price per person?
If necessary, round your answer to the nearest cent.

Steps I took:

I realized that the expression to describe the relationship would be $50x+1000$. However, they gave me more information by saying that the bride, groom and $10$ close family members will be attending for sure. This allowed me to alter the expression to $50x+1600$. 

I also know that the price per person is an independent variable and should be represented by the horizontal axis. However, the second part is not as clear to me. I don't understand what they mean when they say "valid values for the price per person".