Answer:
Step-by-step explanation:
An exponential decay function is generally given in the below;
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;
When t = 8, let's go ahead and solve for y;