Answer:
C
Explanation:
How do we get from 4 to 20? Multiply 4 * 5 = 20.
How do we get from 20 to 100? Multiply 20 * 100.
Thus the answer is C where you multiply 5 by the previous function output.
I saw this pattern from experience, however you could also solve another way:
Simply plug in to the given functions in each answer choice.
For example, A:
f(1) = 4
f(n) = 16 * f(n - 1), for n >= 2
Now test values of n and check if they match the table.
f(1) = 4. This matches the table
f(2) = 16 * f(2 - 1) = 16 * f(1) = 16 * 4 = 64. This does not match the table.
You continue this process with the rest of the answer choices until you find a function, f(n), that gives the correct output of the table.