Answer
The amplitude is $~~0.15~cm$
Work Step by Step
In part (b) we found that the block reaches a point $0.10~m$ above the unstretched point, and the block reaches a point $0.20~m$ below the unstretched point.
The distance between the highest point and the lowest point is $0.30~m$
The amplitude is half of this distance.
Therefore, the amplitude is $~~0.15~cm$
