Answer: 
Step-by-step explanation:
The rate of change is a measure in which one variable is modified in relation to another. In this case we have the variables:
Temperature in 
Time in 
Now, to calculate the rate of change, we have to divide one variable by the other. In this case the change in temperature
divided by the time variation
.
Hence, assuming the ambient temperature of the glass is
and the elapsed time
we have:

(8 2/3) / (2/3) = x / 1....8 2/3 miles to 2/3 hr = x miles to 1 hr
cross multiply
(2/3)(x) = (8 2/3)(1)
2/3x = 26/3
x = 26/3 * 3/2
x = 26/2...which equals 13....she will ride 13 miles in 1 hr
$ 40 ..... 100 %
$ 28 ..... x %

The % of change is 70 %.
This is equivalent with:
- the final price ($ 28) is 70 % from the initial price ($ 40)
- the initial price ($ 40) was reduced with 30% giving the new price as: