Number Series Questions

In the following series, one number is missing as shown by the question mark. Select the missing number from the given options.

8, 12, 16, 20, ?

A series is given with one term missing. Choose the correct alternative from the given ones that will complete the series.
1, 7, 42, 210, 840, ?

A series is given with one term missing. Select the correct alternative from the given ones that will complete the series.
2, 7, 16, ? , 46, 67

In the following series, one number is missing as shown by the ?. Select the missing number from the given options.

3, 8, 13, 18, ?