$\ (-25) . (-3) . 4$
$\ =[(-25) . 4] . (-3)$
$\ = (-100) . (-3) = 300$
.
$\ (-1) . (-4) . 4 . 8 . 25$
$\ = (4 .25) . {[(-1) . (-4)] . 8}$
$\ = 100 . 32 = 3200$
.
$\ 2 .4.(-6)^{2} : 12$
$\ = 8 . 12 : 12$
$\ = 8$
.
$\ [(-25) . (-27).4] : (-9)$
$\ = 2700 : (-9) = 300$
.
$\ (a^{2} - b^{2}) : (a+b)(a-b)$
$\ = (a^{2} - b^{2}) : [(a + b) . a - (a+b) . b]$
$\ = (a^{2} - b^{2}) : [(a^{2} + ab) - (ab + b^{2})]$
$\ = (a^{2} - b^{2}) : (a^{2} - b^{2}) = 1$