Answer for a)
Since the coordinates are arranged as (x, y, z), then 3 would be for x, 0 would be for y, and 1 would be for z. The x is the length, the y is the height, and the z is the width. It is said that the x-axis value is 3 so there are 4 letters on the 3 value which are: P, S, B, and A. Now, let's look at the 0 on the y-axis. Since the y-axis is the height, then there are 2 letters remaining: A and B. Now, the z-axis is 1. So the letter for point (3, 0, 1) is... B.
Answer for b)
For the x-axis, P is at 3. For the y-axis, P is at 2. For the z-axis, P is at 1. So the coordinate of P is: (3, 2, 1).