If the factors of a polyomials are
[tex]\begin{gathered} (x+3) \\ (x+12) \end{gathered}[/tex]This means that the polynomial can be written as a power of thouse factors, like:
[tex]P(x)=(x+3)^n(x+12)^m[/tex]As we can see, if either of the factors zeros out, the hole polynomial you be zero too, because anything will be multiplied by zero.
So, to find the values of x that will make this polynomial equal to zero, we just solve the equation of each factor equal to zero.
So, the first possible x value is:
[tex]\begin{gathered} (x+3)=0 \\ x+3=0 \\ x=-3 \end{gathered}[/tex]And the second possible value of x is:
[tex]\begin{gathered} (x+12)=0 \\ x+12=0 \\ x=-12 \end{gathered}[/tex]Thus, the possible values of x that make the polynomial zero are -3 and -12, which corresponds to alternative C.