Question

A new video game is expected to sell 100 copies the first hour at a local game store. After that, the sales will follow the function s(x) = 12(x − 1) where x is the number of hours. What is the function that shows total sales, including the first hour?
s(x) = 12(x − 1) − 100

s(x) = 100x − 12

s(x) = 100 − 12(x − 1)

s(x) = 100 + 12(x − 1)

Answer 1

To answer this you need to make simple thought experiment. Since the number of sales after time passes cannot go negative (note that rate at which copies are sold can drop over time but total number cannot) that means that you are adding number of sales at first hour and during first hour.

first option cannot be the answer because you are subtracting 100 copies to total number of sold copies which is not logical.

The answer is D)   s(x) = 100 + 12(x-1)
after 1 hour (if you replace x with 1 in equation above) you will get 100 copies which matches conditions in the text.