What letters will fill the blank?

Z, X, V, T, R, __,__

In the following question, select the missing number from the given series.

23, 29, 24, 30, 25, ?

In the following question, select the missing number from the given series.

64, 73, 83, 94, ?, 119

In the following question, select the missing number from the given series.

567, 189, 63, ?, 7

In the following question, select the missing number from the given series.

119, 121, 124, 128, ?, 139

In the following question, select the missing number from the given series.

13, 17, 26, 42, 67, ?

In the following question, select the missing number from the given series.

1, 2, 4, 7, 11, ?

In the following question, select the missing number from the given series.

13, 22, 66, ?, 225, 234, 702, 711

In the following question, select the missing number from the given series.

6, 13, 20, 27, ?