Question

0 4 10 20 50 80 105 displacement time 0 1 2 3 6 9 12

Answer 1

not sure just what you are after here, but the average velocities over each interval are
4/1 6/1 10/1 30/3 30/3 25/3
or
4.0 6.0 10.0 10.0 10.0 8.3

Or, the average velocity for the whole accumulated interval is
4/1 10/2 20/3 50/6 80/9 105/12
=
4.0 5.0 6.3 8.3 8.9 8.8

you go ahead and decide how you want to use this