The mapping diagram shows a functional relationship

f(x) = 4 when x equals 8. The domain consists of the set of x values that render the function valid. Allowed x values correspond to function mapping. Conversely, the range refers to the y values that constitute the function's defined area. In seeking f(a), we check where "a" resides in the domain to find its mapping in the range. If we need the x value that corresponds to f(x) = a, we identify the given a in the range to locate the corresponding x in the domain. Thus, to find f(4), we investigate where "4" is situated in the domain. Following this logic, we conclude that f(8) yields 4.