Kinematics of motion in a straight line — practice question

The displacement of a particle after it has left a fixed point $O$ at time $t$ is $s$ m. The diagram presents a displacement-time graph that represents the particle's motion. The graph is made up of $4$ straight line segments. In the first $10$ s, the particle covers $50$ m, then it moves at $2\,\text{m s}^{-1}$ for $10$ s. After that, the particle remains at rest for $20$ s, before it gets back to its starting point when $t = 60$.