Daniel B. answered 12/14/20
A retired computer professional to teach math, physics
Let me rephrase the question.
We are told that f(2) = -8.
We are given g(x) = f(-x+5)+7.
The question is "For what value x can be determine g(x)".
The answer is that x must be such that
-x+5 = 2
That is
x = 3
And
g(3) = f(2)+7 = -8+7 = -1.
The coordinates sought in the original question are (3, -1).