Answer
$(x-2)(x+2)(b+a)$
Work Step by Step
$ bx^{2}-4b+ax^{2}-4a\qquad$...factor in pairs.
$=(bx^{2}-4b)+(ax^{2}-4a)$
$=b(x^{2}-4)+a(x^{2}-4)$
$=(x^{2}-4)(b+a)\qquad$...recognize the difference of two squares: $a^{2}-b^{2}=(a-b)(a+b)$
$=(x-2)(x+2)(b+a)$
