Question 515147
<pre>
{{{(matrix(6,1,
The_number,
of_ways_to, 
arrange_them,
whether_B_is,
in_second,
place_or_not))-

(matrix(6,1,
The_number,
of_ways_to, 
arrange_them,
with_B_in,
second,
place))}}}

4×3×2×1 - 3×2×1    [or 4! - 3!]
     24 - 6
       18

Here they all are:

 1.  A C B D
 2.  A C D B
 3.  A D B C
 4.  A D C B
 5.  B A C D
 6.  B A D C
 7.  B C A D
 8.  B C D A
 9.  B D A C
10.  B D C A
11.  C A B D
12.  C A D B
13.  C D A B
14.  C D B A
15.  D A B C
16.  D A C B
17.  D C A B
18.  D C B A

Edwin</pre>