Explanation
Let the five positions from left to right be represented as 1, 2, 3, 4, and 5.
From the clues, R is second to the left of Q and to the immediate right of A. This gives the relative sequence A, R, _, Q. Since there are five planes in total, this four-plane block must occupy either positions 1 to 4 or positions 2 to 5.
If the block occupies positions 2 to 5, the remaining two planes, B and P, must occupy position 1 and the blank space at position 3. Since B cannot be at either of the ends, B would have to occupy position 3, leaving P at position 1. This would make P and Q non-neighbours, violating the condition that P and Q are neighbours.
Thus, the block A, R, _, Q must occupy positions 1 to 4:
Position 1: A
Position 2: R
Position 3: Blank
Position 4: Q
Position 5: Remaining plane
The remaining planes B and P must occupy positions 3 and 5. Since B cannot be at any of the ends, B must occupy position 3 and P must occupy position 5. This arrangement satisfies all conditions: B is not at an end, there is exactly one plane (Q) between B and P, and neighbours P and Q are adjacent at positions 4 and 5.
This results in the complete sequence from left to right: A, R, B, Q, P. Therefore, plane A is at the left end.