==> Object A travels for 60 seconds before Object B starts out.
==> Object A moves at 2 m/s.
==> So Object A has a lead of 120 m when Object B starts out.
==> Object B moves at 3 m/s . . . 1 m/s faster than Object A.
==> So Object B catches up on Object A by 1 m every second.
==> Object B closes up Object A's lead of 120 m in 120 seconds.