A 4-letter code word consists of letters O, U, AND P. If the code includes all the three letters, how many such codes are possible?	Choose the correct choice.
A) 72 B) 48 C) 4 D) 84 E) 36
Note that the correct answer to this question is 36, not 72.   O-OUP can be arranged in 4!/2!=12 ways;   U-OUP can be arranged in 4!/2!=12 ways;   P-OUP can be arranged in 4!/2!=12 ways;   Total:  12+12+12= 
<gadget id="calculator"> 12+12+12</gadget>
<output>36</output>
36.   Answer: 36
<result>E</result>
A 4-letter code word consists of letters O, U, AND P. If the code includes all the three letters, how many such codes are possible?