The sums of which two pairs from the table will give you the same result? For example, A + B = C + D.
This is just a tedious exercise:
-4 + 9i + 6 - 6i == 11-12i + (-9+15i)
2 + 3i == 2 + 3i
Honestly, this is just a bash.
test test test.
+36916 
