Go through this post first to understand the theory of Functions!

\(f ( x ) = 3( x + 2) + 5\) is given to us and we need to find the value of \(f ( a − 2) =\).
To solve this we will compare what is inside the bracket of the question
so, (a-2) is asked and in the question we are (x)
so, in \(f ( x ) = 3( x + 2) + 5\) we need to replace x with a-2 to get the value of \(f ( a − 2)\)
=> \(f ( a − 2) =\) = 3*((a-2) + 2) + 5 = 3*a + 5

So, Answer will be B
Hope it helps!