Question

Find the object's speeds v1, v2, and v3 at times t1=2.0s, t2=4.0s, and t3=13s.

Answer 1

Since this is a distance/time graph, the speed at any time is the slope
of the part of the graph that's directly over that time on the x-axis.

At time  t1 = 2.0 s
That's in the middle of the first segment of the graph,
that extends from zero to 3 seconds.
Its slope is  7/3 .              v1 = 7/3 m/s .

At time  t2 = 4.0 s
That's in the middle of the horizontal part of the graph
that runs from 3 to 6 seconds.
Its slope is zero.
                                     v2 = zero .

At time  t3 = 13 s.
That's in the middle of the part of the graph that's sloping down,
between 11 and 16 seconds.
Its slope is  -3/5 .            v3 = -0.6 m/s .              

Answer 2

The slope or gradient of a line is a number that describes both the direction and the steepness of the line. For a distance-time graph, it signifies the velocity.

at t1=2.0s
v =  7/3 m/s 

At time  t2 = 4.0 s
v = zero

At time  t3 = 13 s
v = -0.6 m/s

Hope this answers the question. Have a nice day.