21. MODELING WITH MATHEMATICS The value
mountain bike v (in dollars) can be approximated
the model v = 200(0.75), where t is the number of
vears since the bike was new. (See Example 2.)
a. Tell whether the model represents exponential
growth or exponential decay.
b. Identify the annual percent increase or decrease in
the value of the bike.
c. Estimate when the value of the bike will be $50.