Field is not zero

A point charge $q$ is located at the center of a thin ring of radius $r$ with uniformly distributed charge $-q$ . Find the magnitude of the electric field strength vector at the point lying on the axis of the ring at distance $x$ from its center with $x >> r$ .

If the answer is in the form of $\frac {aq r^b}{c\pi} \epsilon(x^d)$ for positive integers $a,b,c,d$ with $a$ and $c$ coprime, give your answer as $a+b+c+d$ .