Answer:
They must sell 720 books.
Explanation:
Let x be the number of year books that they must sell before their business breaks even.
Given,
The cost price of each year book = $ 5
The cost price of x books = 5x dollars,
Also, the investment = $ 18000,
Thus, the total cost of the x books = ( 5x + 18000 ) dollars
Now, the selling price of the book = $ 30,
So, the total revenue = The total selling price of x books = 30x
In the case of break even,
Total revenue = Total cost
⇒ 30x = 5x + 18000
Subtracting 5x on both sides,
30x - 5x = 18000
⇒ 25x = 18000
Divide both sides by 25,
x = 720
Hence, they must sell 720 yearly books before their business breaks even.