What information is missing but is needed to solve this problem?

the community theater staged performances on friday, saturday, and sunday. there were 357 people at friday's performance and 422 at sunday's performance. how many people attended saturday's performance?

a.
the number of people at friday's, saturday's, and sunday's performances combined

b.
the number of people at friday's and sunday's performances combined

c.
the difference between the number of people at friday's and sunday's performances

d.
the average of the number of people at friday's and sunday's performances