Question 844040
Velocity is distance divided by time.
At 5 sec, you traveled 50 meters.
{{{v[a]=50/5=10}}}m/s
At 10 sec, you have traveled 100 meters and stopped. 
So at 15 sec, you are moving at {{{v[b]=0}}} m/s.
At 20 seconds you start moving again, and by 25 sec you have traveled 0-100=-100 meters in 5 sec.
{{{v[c]=-100/5=-20}}} m/s
At 30 secs you start moving in the opposite direction and by 35 sec have travel -50-(-100)=50 meters in 5 sec.
{{{v[d]=50/5=10}}} m/sec.
You are basically measuring the slope of the lines.
The slopes for A and D are equal (visually) so the velocities are equal.
The slope in C is much steeper (greater) and in the other direction (negative).
The slope in B is zero. You are not moving.