Your answer is partially correct.
The figure shows a ring of outer radius R = 16.0 cm, inner radius $r = 0.200R$, and uniform surface charge density $\sigma = 1.10 \text{ pC/}m^2$. With V = 0 at infinity, find the electric potential at point P on the central axis of the ring, at distance $z = 1.80R$ from the center of the ring.