What letters will fill the blank?

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

What will come in place of the question mark (?) in the following number series?11, 19, 40, 87, 173, ?

In the following question, select the missing number from the given series.
2, 5, 17, 71, ?

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

9, 11, 14, 18, 23, ?

In the following question, select the missing number from the given series.
19, 26, 45, 71, 116, ?

Select the missing numbers from the given alternatives

8  21  4

27 ?   53

A series is given, with one term missing. Choose the correct alternative from the given ones that will complete the series.

5 , 10 , 30 , ? , 600 , 3600

In the following question, select the missing number from the given series.
3, 8, 5, 27, 8, 64, 12, 125, 17, ?

In the following question, select the missing number from the given series.
21, 25, 52, 68, 193, ?