Question

A bookstore costs $90 a day to keep open, and spends $12 for each book it sells. the store charges $18 for each book it sells. If n represents the number of books sold, which equation represents the revenue function for this bookstore?

Answer 1

Total Cost in a day is $TC= 90 + 12n$. Profit function is $P=18n$. And the revenue function is $R = P-TC = 18n-12n-90 = 6n-90$. In a day, bookstore must sell at least 15 books, because of 6n-90=0, in order to make profit. 

Answer 2

Answer:

$R=6n-90$

Step-by-step explanation:

Let

R------> the revenue function

n------> the number of books sold per day

we know that

In this problem

$18n$ -----> represent the profit

$(12n+90)$ -----> represent the cost

so

The revenue is equal to the profit minus the cost

$R=18n-(12n+90)$

$R=n(18-12)-90$ ------> equation that represent the revenue function

Simplify

$R=6n-90$