Answer
$(x-3)(x+4a)$.
Work Step by Step
The given polynomial is
$= x^2-3x+4ax-12a$
Group the terms.
$= (x^2-3x)+(4ax-12a)$
Factor each group.
$= x(x-3)+4a(x-3)$
Factor out $(x-3)$.
$= (x-3)(x+4a)$
Hence, the factor of the polynomial is $(x-3)(x+4a)$.
