As I can see it , there are 4 straight lines. So here is what i suggest :-

Write the equations to each of these 4 lines. So you have 4 equations f(x,t) (x- distance and t - time)

now for each find dx/dt .

So now you have the velocity function (v=dx/dt) with the corresponding time limits, for example the first line goes from t=0 to t=15

Plot the 4 velocity functions accordingly.

Hope that helps !