1.

my $b_count = () = map { grep { $_ eq "b" } @$_ } values %{$Hash{Compa
+ny_A}};
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This iterates over values of anonymous hash referenced in $Hash{Company_A}, which are anonymous array references, and returns a list of "b" values, which, assigned to a scalar, transforms to the count of the values. Untested, but should work.

Sorry, I couldn't understand your second question. Perhaps reading perlreftut will help you solving it yourself.