It may be
>! Since it is mental arithmetic and no restrictions
>! 3, -3, 4i, -4i since a) 3 -3i =0  b) 3 + 4i = (2 + i)(2 + i)  c) 3 - 4i = (2 - i)(2 - i)  d) -3 + 4i = (1 + 2i)(1 + 2i)  e) -3 - 4i = (1 - 2i)(1 - 2i)  f) 4i - 4i = 0  and also 3 - 3 + 4i - 4i =0     (Apologies for the formatting)