Hallo,
(6 + 17i) · z + (−4 + 17i) = 102 − 116i | - (−4 + 17i)
(6 + 17i) · z = 102 − 116i - (−4 + 17i)
(6 + 17i) · z = 102 − 116i +4 - 17i
(6 + 17i) · z = 106 − 133i |:(6 + 17i)
z = (106 − 133i) /(6 + 17i) *(6-17i)/(6-17i)
= (-1625 -i 2606)/325
= -5 -8i