Me with graphing this
explain

She must start out going 8 miles per hour until the time elapsed is 1 hour at which time she drops 1.5 miles per hour. The same happens again in the second hour and the third.

The graph must have hours on the x axis and speed on the y axis.

The starting point is (0,8)

The graph must be

y = 8 - 1.5x

You need three points.

x                  y

0                 8

1                  6.5

2                  5