Explanation:

Let’s break it down in plain English:

- There are six people: Mr A, Mr B, Mrs C, Miss D, Mr E, and Miss F.

- There are six roles: manager, assistant manager, cashier, stenographer, teller, and clerk.

- The assistant manager is the manager’s grandson. So, the assistant manager must be male, and young enough—can’t be a woman.

- The cashier is the stenographer's son-in-law. This means cashier is male, married to the stenographer’s daughter.

- Mr A is a bachelor. So, he can’t be anyone’s son-in-law.

- Miss D is the teller’s step-sister. D is female, so can’t be the cashier or assistant manager (both are definitely male by logic above).

- Mr E is manager’s neighbour. This doesn’t immediately pin him down, but suggests he’s not family.

- Mr B can’t have a grandson or son-in-law—he’s just 20 years old.

Now, the question: Who’s the assistant manager?

Option 1: Mr A—He’s a bachelor, so can’t be married, but nothing here says he can’t be a grandson. Maybe possible.

Option 2: Miss F—Can’t be, assistant manager must be male (the “grandson” clue).

Option 3: Mrs C—She’s a “Mrs,” so not a “grandson.”

Option 4: Mr B—Here’s the thing, Mr B is only 20 and can’t have a grandson, but he himself could be one! And the clue says the assistant manager is the manager’s grandson, so Mr B can fit.

But...

- The options want “Who is the assistant manager?” and given the clues, Mr B is the only one who is male, young (to be a grandson), and not disqualified by the other rules.

So, the correct answer is:

Option:4, Mr B

Summary:

- Mr B is young, eligible to be someone’s grandson (assistant manager).

- Mr A is a bachelor—so he can’t be any married position or have in-laws, but that wasn’t needed here.

- Assistant manager must be male; only possible is Mr B.

So, Mr B is the assistant manager.