Final answer:
The total number of people who visited the arena on Friday and Saturday is 21,428.
Step-by-step explanation:
The total number of people who visited the arena on Friday and Saturday can be found by adding the number of people who attended the concert on Friday and the number of people who attended the rodeo on Saturday.
Given that 12,211 people attended the concert on Friday and 9,217 attended the rodeo on Saturday, the total number of people who visited the arena is 12,211 + 9,217 = 21,428.