Select the number from among the given options that can replace the question mark (?) in the following series.

30, 20, ?, 60, 140​​

Given: ​30, 20, ?, 60, 140​​

Logic: Each number follows the pattern: (Previous number × Increasing multiplier 0.5, 1, 1.5, 2, ...) + Increasing addition value 5, 10, 15, 20, ....​

(30 × 0.5) + 5 = 15 + 5 = 20 

(20 × 1) + 10 = 20 + 10 = 30 (Missing number = 30)

(30 × 1.5) + 15 = 45 + 15 = 60 

(60 × 2) + 20 = 120 + 20 = 140 

Thus, correct option is (a).