After 1 minute, a file Portia is downloading
from the internet is at 0 kilobytes
downloaded. After 2 minutes, the file is
at 3 kilobytes downloaded. After 3 minutes,
the file is at 8 kilobytes downloaded.
After 4 minutes, the file is at 15 kilobytes
downloaded. Write an expression to model
the amount of the file downloaded.
Explain your reasoning.