Let z1=x1+iy1,z2=x2+iy2
z1−z2=(x1−x2)+i(y1−y2)
∵arg(z1−z2)=4π⇒tan−1(x1−x2y1−y2)=4π
⇒y1−y2=x1−x2−−−−(1)
∣z1−3∣=Re(z1)⇒(x1−3)2+y12=x12
∣z2−3∣=Re(z2)⇒(x2−3)2+y22=x22
⇒(x1−3)2−(x2−3)2+(y12−y22)=x12−x22
⇒(x1−x2)(x1+x2−6)+(y1−y2)(y1+y2)=(x1+x2)(x1−x2)
⇒x1+x2−6+y1+y2=x1+x2
⇒y1+y2=6