The table and the numbers might be a little intimidating but this is actually just a speed-distance-time problem. When we say average rate, we mean average speed, in this case.
Here is the solution:
[tex]average speed = \frac{350-126}{5-3} = 112 \frac{ft}{s} [/tex]
This represents the average speed of the system. If we plot the table, the speed represents the slope of the line.
