Multiply numerator and denominator by the conjugate of the denominator
Denominator: -10 + 8i
Conjugate of the denominator: -10 - 8i
Operation:
[9 +7i] / [-10 + 8i] * [-10 -8i] / [-10 - 8i] = [-90 - 72i - 70i +56] / [100 + 64] =
[-34 -142i] / 164 = [-17 -71i] / 82