factor because if we have
yz=0 then we can assume y and/or z=0
so factor
so the easiest way is to find what 2 numbers add to -6 and multiply to get 9 so
we know that they must be both - because we must have x+x=(-) and x^2=+ so therefor they must be negative
factors of 9=3 and 3 so
-3 and -3
-3+-3=-6 perfect
(z-3)(z-3)=0
set each to zero
z-3=0
add 3
z=3
z=3 is the answer