Answer:
x = - 5
Step-by-step explanation:
Given
f(x) = 
The denominator of f(x) cannot be zero as this would make f(x) undefined. Equating the denominator to zero and solving gives the value that x cannot be.
solve : 3x + 15 = 0 ⇒ 3x = - 15 ⇒ x = - 5 ← excluded value
Domain x ∈ R , x ≠ - 5
The correct answer is option D.
F(G(x)) denotes the composition of the two functions F(x) and G(x). The composition of two functions result in x, if the two functions are inverses of each other. So in this case F(x) and G(x) will be the inverse of each other. So option D is the correct answer.
Theorem: If two chords intersect within a circle, then the product of the lengths of the segments (parts) of one chord is equal to the product of the lengths of the segments of the other chord.
In oyur case,

Solve this equation to find x:

Answer: 6, choice B.