For a class photo, a group of students forms a single line from left

To get the correct approach, we assume we are facing the group of students in line. Therefore, the terms “left” and “right” are from our perspective.

Let’s first work from the left. Since Robert is the 15th student from the left and Christine is immediately to the left of Robert, there must be 13 students to the left of Christine (so that Christine is 14th and Robert is 15th in line from the left).

Now let’s work from the right. Since Christine is the 13th student from the right and Robert is immediately to the right of Christine, there must be 11 students to the right of Robert (so that Robert is the 12th and Christine is the 13th from the right). To recap, we have, from left to right:

13 students, Christine, Robert, 11 students

Therefore, there must be 13 + 1 + 1 + 11 = 26 students in the line for the class photo.

Answer: A