well if it asks you to send to 4 people and there are 8 generations which includes yours that mean
1 sent to 4 - 4 recived
4 send to 4 each = 16 recived + the 4 before = 20 (generation 2)
16 send to 4 = 64 + 20 = 84 (generation 3)
64 send to 4 = 256 + 84= 320 (g4)
256 send to 4 = 1024 + 320 = 1344 (g5)
1344 s t 4 = 5376 + 1344= 6730 (g6)
so on and so forth till generation 8
I'm assuming this is multiple choice and you forgot to post the answers. I'll take a guess and say it probably looks something like this:

Because you can't take the square root of a negative number without getting an imaginary result, resulting in the function having a closed domain limit.