Complete the series: 3, 6, 11, 18, ?, 42.

B. 28

Complete the series: B, D, F, H, ?

A. J

Find the missing number in the series: 5, 10, 20, 40, ?

C. 80

What is the next letter in the series: A, E, I, M, ?

A. O

What letter comes next in the series: a, e, i, o, ?

A. U