At a bus stop row, A is 7th from the left and B is 9th from the right. After interchanging their positions, A becomes 11th from the left. How many people are in the row?

Introduction / Context:
Converting a right-side rank to a left-side position uses N − r + 1. Swapping places means A assumes B’s original position.

Given Data / Assumptions:

• B is 9th from right in a row of N; hence B’s left-rank is N − 9 + 1 = N − 8.
• After the swap, A’s left-rank is 11 (i.e., A occupies B’s former position).

Step-by-Step Solution:

Verification / Alternative check:
Check that a 9th-from-right position is indeed 11th from left when N = 19.

Final Answer:
19