Identify the type of function represented by f(x)=3/8(4)x

We have the following function:
 f (x) = 3/8 (4) ^ x
 The function is of the form:
 f (x) = A (b) ^ x
 Where,
 A: initial amount
 b: growth factor (b> 1)
 x: time variable.
 
 f (x) = 3/8 (4) ^ x
 It is an exponential function of the form:
 f (x) = A (b) ^ x