Answer:
[tex]x=-6, \: x=3[/tex]
Step-by-step explanation:
[tex]f(x)=x^2+3x-18\\\\0=x^2+3x-18\\\\0=(x+6)(x-3)[/tex]
[tex]x+6=0\\\\x=-6[/tex]
[tex]x-3=0\\\\x=3[/tex]
Remember to separate the factors into 2 equations to get each individual root/solution by the Zero Product Property!