"Sum" of the functions are interesting

• $f_k (x)$ has three roots and they are $k$ , $-k$ and $0$ , where $k$ is a real positive integer $\geq 1$ . Which of the followings (in terms of $n$ ) is the value of $x$ when $f_1 (x)+f_2 (x)+\cdots+f_n (x)=0$ ?
• Assume all $f_k (x)$ has equal real constant $d$ , such that $f_k (x)=d(x)(x-k)(x+k)$ where $d$ is not $0$
• Given that $x>0$ and $n=24$ ,
• express your answer in the form $\dfrac{a \sqrt b}c$ , where $a,b$ and $c$ are positive integers with $a,c$ coprime and $b$ square-free.

Submit your answer in the form $a+b+c$ .