The series alternates between letters from the beginning of the alphabet and letters from the end, specifically pairing 'a' with 'z', 'b' with 'y', 'c' with 'x', and 'd' with 'w'. Following this pattern, after 'd', the next letter should be 'w'. Hence, the next letter in the series is 'w'.
d
It's the letter D of course! Haven't you heard of Jason D?!
T
D
The next letter should be "S".
The next (and last) letter is C. Just as a countdown counts backwards, this series is "countdown" spelled backwards.
g.
K
E
The series appears to be following a pattern where the letters are increasing in alphabetical order, skipping some letters. The pattern is A (skipping B) D (skipping E, F, G, H, I, J, K, L, M, N) O (skipping P) Q. Therefore, the next letter in the series should be R.
For bills with no series letter next to the date, or A through D, face value to $140 depending on how worn it is. For bills with an E series letter, $140 to $200.