Answer:
When the input is 4, the output of f(x) = x + 21 is 25.
Explanation:
The given function is
Here, x is input and f(x) is output.
We need to find the output of the given function f(x) if the input is 4.
Substitute x=4 in the given function.
So, the output value is 25.
When the input is 4, the output of f(x) = x + 21 is 25.