Answer:
z + 15
Step-by-step explanation:
[tex] {z}^{2} + 9z - 90 \\ \\ = {z}^{2} - 6z + 15z - 90 \\ \\ = z(z - 6) + 15(z - 6) \\ \\ = (z - 6)(z + 15) \\ [/tex]
