Here is the correct arrangement to fill in the blanks:
A function is a rule that relates inputs to outputs.
An input is also called a(n) x-value.
An output is also called a(n) y-value.
In a function, each input is paired with exactly one output.
So, the filled text would look like this:
A function is a rule that relates inputs to outputs.
An input is also called a(n) x-value.
An output is also called a(n) y-value.
In a function, each input is paired with exactly one output.