Find number of restriction fragment size in chromosome

[kanagasundar]

Hi all,
I am prepare in entrance exam. I need help.
A restriction endonuclease has the recognition sequence G/AATTC, where "/" indicate the cut side. This sequence is found, on average, once every 'X' residues in a chromosome. 'X' =
Options
a. 146 base - pairs
b. 200 base - pairs
c 256 base - pairs
d. 4096 base - pairs
advance thanks reply as soon as possible

[JackBean]

how many combinations of six consecutive nucleotides can you have?