Assume their age ratio is $x$
then age of 3 person is $4x$,$7x$ ,$9x$
According to the question,$8$ year ago the sum of their age was $56$
$\Rightarrow (4x-8)+(7x-8)+(9x-8)=56$
$\Rightarrow 20x-24=56$
$\Rightarrow 20x=80$
$\Rightarrow x = 4$
Now their present age is $16,28,36$, Option B.