Answer:
Step-by-step explanation:
I am assuming that you are asking what is [x] - 5 if f(86).
When you have this kind of question, what you do is to substitute the variable inside the parenthesis, so like what is says, f(x). If the question replaces the variable x with 86, that means you input the number into the equation.
So [x] - 5, if f(86).
Substitute:
86 - 5