A teacher is traveling at 4 m/s when he (Mass A = 150 kg) runs into a student (Mass B =100) who is standing still (velocity =0). If the teacher is traveling at 3 m/s (VA2) how fast is the student traveling at (VB2)?

Use the conservation of momentum: M_a * V_{a1} + M_b * V_{b1} = M_a * V_{a2} + M_b * V_{b2}, where the index "a" refers to the teacher, "b" refers to the student.

Note that the speed of the teacher after the collision will be larger than the speed of the student, so they will need to change places (at first teacher was to the left of the student, then to the right) which is not possible as a result of the collision. It looks like the data are contradictory within the selected model.