Answer
$\color{blue}{(m^4+3)(2-a)}$
Work Step by Step
Regroup:
$=(2m^4+6)+(-am^4-3a)$
Factor out $2$ in the first and $-a$ in the second group to obtain:
$=2(m^4+3)+(-a)(m^4+3)$
Factor out $m^4+3$ to obtain:
$(m^4+3)[(2+(-a)]
\\=\color{blue}{(m^4+3)(2-a)}$