An astronaut drops a rock into a crater on the moon the distance d(t), in meters, the rock travels after t seconds can be modeled by the function d(t)= .8t^2.what is the average speed in meters per second of the rock between five and 10 seconds after it was dropped

  speed = distance/time
The average speed will be the change in distance divided by the change in time.
  (d(10) -d(5))/(10 -5) = (80 -20)/5 = 12 . . . . meters per second

The plan is 100 songs downloaded equally on each week for 5 weeks, so,

100 songs/ 5 weeks; 20 songs per week.

Number of Weeks (x)              Songs left to download (y)
            1                                                  100
            2                                                  80
            3                                                  60
            4                                                  40
            5                                                  20 

The rate of change is 20 songs per week. 

y = mx + b, input in the STAT feature of the calculator.

m = -20
b = 120