Plz help plz ill give brainliest

A scientist is growing bacteria.

The number of bacterial cells triples every week.
There are currently 20 cells.

Which expression shows how to find the number of cells in 4 weeks?
A. f (4) = 3 ∙ 204
B. f (4) = 4 ∙ 203
C. f (4) = 20 ∙ 34
D. f (4) = 20 ∙ 43