Answer:
[tex]y=57(0.88)^t[/tex][tex]\text{ \$}20.50[/tex]
Explanation:
An exponential decay function is generally given in the below;
[tex]y=a\cdot(1-r)^t[/tex]
where a = initial amount
r = percentage rate of decrease in decimal
t = number of years
Given the initial value of the book(a) as $57 and the percent decrease(r) as 12% which as a decimal is 0.12 (12/100), let's go ahead and substitute these values into the above formula and we'll have;
[tex]\begin{gathered} y=57(1-0.12)^t \\ y=57(0.88)^t \end{gathered}[/tex]
When t = 8, let's go ahead and solve for y;
[tex]\begin{gathered} y=57(0.88)^8 \\ y=\text{ \$}20.50\text{ (to the nearest cent)} \end{gathered}[/tex]
