Orthogonal stability of a cubic-quartic functional equation

Using fixed point method, we prove the Hyers-Ulam stability of the orthogonally cubic-quartic functional equation f(2x + y) + f(2x - y) = 3f(x + y) + f(x - y) + 3f(x -y) + f(y - x) + 18f(x) + 6f(-x) -3f(y) - 3f(-y) for all x, y with x ┴ y.