Which expression represents the sum of the complex numbers z1=6+2iz_1 = 6 + 2iz1=6+2i and z2=−3+4iz_2 = -3 + 4iz2=−3+4i?
3+6i3 + 6i3+6i
3−2i3 - 2i3−2i
9+6i9 + 6i9+6i
9−2i9 - 2i9−2i