3 were called on Friday. Then the each of the 3 called 3 others which all equals to 9, since 3*3 is 9. Now, each of the 9 called 3 others on Sunday which altogether equals 27, since 9*3 is 27. Therefore, the answer is 27.
Every time the word each is used in a math problem, that would mean that you need to multiply something. And that's what happened here
