Final answer:
The appropriate domain for this function is non-negative real numbers.
Step-by-step explanation:
The appropriate domain for this function is 3) Non-negative real numbers.
Since the age of the machine cannot be negative, the domain must be restricted to non-negative real numbers, meaning x can be any non-negative value. In this case, x represents the age of the machine in years, and it cannot be negative since the machine cannot have negative age.
For example, if the machine is 10 years old, the value of the machine can be calculated by substituting x=10 into the function:
f(10) = 16(4/5) = 12.8 thousand dollars.