If all of the telephone extensions in a certain company must be even numbers, and if each of the extensions uses all four of the digits 1, 2, 3, and 6, what is the greatest number of four-digit extensions that the company can have?	Choose the correct option:
A) 4
B) 6
C) 12
D) 16
E) 24
The four digits available are 1,2,3 and 6   as the extensions can only be even numbers, the last digit has to be either 2 or 6   If it is 2...it leaves 1,3 and 6 for the first three digits...these can be arranged in 3! ways   If the last digit is 6...it leaves 1,2 and 3 for the first three digits...these can be arranged in 3! ways   Thus answer is 2*3! = 12 12
<result>C</result>
If all of the telephone extensions in a certain company must be even numbers, and if each of the extensions uses all four of the digits 1, 2, 3, and 6, what is the greatest number of four-digit extensions that the company can have?