Three point charges are on the x axis: q₁ is at the origin, q₂ is at x = 3 m, and q₃ is at x = 6 m. Find the potential at the point x = 0, y = 3 m if

(a) q₁ = q₂ = q₃ = 2 μC,

(b) q₁ = q₂ = 2 μC and q₃ = –2 μC, and

(c) q₁ = q₃ = 2 μC and q₂ = –2 μC.