I have no idea on how to solve this problem. Please show me a step by step solution!Quote:

Once the initial publicity surrounding the release of a new book is over, sales of the hardcover edition tend to decrease exponentially. At the time publicity was discontinued, a certain book was experiencing sales of 25,000 copies per month. One month later, sales of the book had dropped to 10,000 copies per month. What will the sales be after 1 more month?

The answer is 4000.

And also need assistance with the following question...

Find $\displaystyle f(2) $ if $\displaystyle f(x) = e^{kx}$ and $\displaystyle f(1) = 20$.

Here's what I did...

$\displaystyle 20 = e^{k \times 1}$

$\displaystyle e^{20} = e^{k \times 1}$

$\displaystyle 20 = e$

$\displaystyle f(2) = e^{20 \times 2}$

$\displaystyle f(2) = 2.3539$ x $\displaystyle 10^{17}$

...and textbook answer is 400.