Where's the information?

Algebra Level 5

\[\large f(20 + x) = f(20 - x)\]

Let \(f:\mathbb{R} \to \mathbb{R}\) such that \(\forall x \in \mathbb{R}\), the above is true. Given that \(f\) has exactly 3 real roots at \(a\), \(b\) and \(c\), find the value of \(a+b+c\).