Dexter travels 2000 m east in 60 s and then he travels 800 m west in 40 s. What is Dexter’s average velocity?

Scientists follow specific processes in order to determine valid explanations and conclusions from observations. david observed strange lights in the sky above his home outside of roswell, new mexico. the only explanation that makes sense to him is that there are ufos in the area. what should david do next to verify his explanation?