By definition, the function is a relation in which each input value (x-value) has one and only one output value (y-value).
In this case, you have the following function:
And you need to find the input value that has the following output value:
In order to find that value of "x", you need to substitute the given ouput value into the function:
And now you must solve for the variable "x". To do it, you must apply the Addition property of equality by adding 11 to both sides of the equation:
The answer is: