Answer:
64
Explanation:
You have the recursive formula f(1)=1; f(n)=4f(n-1) and you want f(4).
Recursion
The value of f(4) can be found a couple of ways. Perhaps the simplest is to compute the first 4 terms of the sequence using the recursive formula.
f(1) = 1
f(2) = 4·1 = 4
f(3) = 4·4 = 16
f(4) = 4·16 = 64
The value of f(4) is 64.
Explicit formula
The multiplying factor of 4 on the previous term tells you this is a geometric sequence with a common ratio of 4. The explicit formula is then ...
f(n) = f(1)·r^(n-1) . . . . . n-th term of sequence with common ratio r
f(n) = 1·4^(n-1) . . . . . . formula for f(1)=1 and r=4
For n=4, this is ...
f(4) = 1·4^(4-1) = 4^3
f(4) = 64