A series is given with one term missing. Select the correct alternative from…

In an alphanumeric series that combines letters and numbers, each component of a term — the first letter, the second letter, and the number — typically follows its own fixed rule (a constant alphabetical shift or a constant arithmetic operation) from one term to the next; the missing term is whichever value satisfies every one of these rules at the same time.

1. The first letter advances by the same forward shift across S → W → A; applying that shift once more to A gives E.

2. The second letter moves by the same backward shift across J → F → B; applying that shift once more to B gives X.

3. The number follows the same multiply-then-add rule across 20 → 42 → 86 (each term = previous × 2 + 2); applying that rule once more to 86 gives 174 (86 × 2 + 2 = 174).

4. Putting the letters and the number together gives the complete missing term, EX174.

Extending the same three rules one further step checks out against the series' final given term, IT350: the letter rules give I (from E) and T (from X), and the number rule gives 350 (174 × 2 + 2) — matching IT350 exactly. This three-way match across all five terms confirms the answer. (An earlier version of this series had printed 370 in place of 350 by mistake; that misprint has been corrected here.)

Hence, the missing term is EX174.