For part i, it is the maximum distance the mass goes, in this case is 20. For part ii, in one cycle the mass returns to position B and is going to start another oscillation in the same direction as it's original motion. It means that one cycle is to and fro Back to its original position, and going to start it's next oscillation in the same way as how it started. One example of oscillating motion is B-A-B-C and then back to B again. Then B-A-B-C-B again. For part iii, it's the position after one half oscillation. Therefore, use 0.25s divide 2. Hope it helps!