Viết phương trình của mỗi chuyển động.

$$\begin{gathered} d_1=60t\left(km\right) \\ {d}_2=180+60t\left(km\right) \\ {d}_3=20t\left(km\right) \end{gathered}$$

$$\begin{gathered} d_1=-60t\left(km\right) \\ {d}_2=180-60t\left(km\right) \\ {d}_3=20t\left(km\right) \end{gathered}$$

$$\begin{gathered} d_1=60t\left(km\right) \\ {d}_2=180-60t\left(km\right) \\ {d}_3=-20t\left(km\right) \end{gathered}$$

$$\begin{gathered} d_1=60t\left(km\right) \\ {d}_2=180-60t\left(km\right) \\ {d}_3=20t\left(km\right) \end{gathered}$$