In Figure what is the net electric potential at the origin due to the circular arc of

Question:

In Figure what is the net electric potential at the origin due to the circular arc of charge Q1 = + 7.21pC and the two particles of charges Q2 = 4.00Q1 and Q3 = ?? 2.00Q1? The arc's center of curvature is at the origin and its radius is R - 2.00 m; the angle indicated is θ = 20.0o.