How to graph x vs t and find average velocity?

[physics newb]

I'm not looking for answers so much, just someone to get me started.
OK, you walk 73.2 m at a speed of 1.22 m/s, and then run 73.2 m at 3.05 m/s along a straight line. What is the average velocity of that problem?
Next I need to graph x vs t for the problem, and indicate how the average velocity is found on the graph. How would that be done.

 

[SGT]

What time does it take to win each distance? What is the total time? What is the total distance?

 

[physics newb]

Well, the total distance is 146.4 m. Would the total time be 84 seconds, (1 min, 16 seconds)? If that's right, what next? Also, what do you mean by the time it takes to win each distance? Thanks in advandce!

 

[radou]

Assuming that both speeds are constant, the time of the walking distance of 73.2 m is 60 seconds, and the time of the equal running distance is 24 seconds. Because the velocities are constant, the function of position x(t) is linear. So, you just have to draw the graph of the function: $$x(t) = \left\{\begin{array}{cc}1.22t, 0 \leq t \leq 60 \\3.05t, 60 < t \leq 84\end{array}\right$$ The average velocity is v = (v1*t1 + v2*t2)/(t1+t2) = (1.22*60 + 3.05 * 24)/(60 + 24) = ...

 

[physics newb]

1.74 seconds
So is that my answer for this problem?
Thanks!

 

[radou]

1.74 meters per second. Yup.