1st set = 4 letters
2nd set = 4x 4 = 16 letters
3rd set = 16 x 4 = 64 letters
4th set = 64 x 4 = 256 letters
5th set = 256 x 4 = 1,024 letters
6th set =1024 x 4 = 4,096 letters
7th set = 4096 x 4 = 16,384 letters
8th set = 16,384 x 4 = 65,536 letters
Each letter cost 2
Total cost = 65,536 x 2 = 131,072