## Task B-2.3.

In online shopping, a package of photocopy paper is 9 kuna cheaper than in a bookstore. In December, the secretary bought 8 more packages online than she bought in November for the same amount of 1440 kn in the bookstore. What is the price of photocopy paper in online shopping?
## Solution.

Let $x$ be the price of a package of paper in the online store.

We can buy $\frac{1440}{x}$ packages in the online store, or $\frac{1440}{x+9}$ in the bookstore.

The difference in the number of packages is $\frac{1440}{x}-\frac{1440}{x+9}=8$,

and solving this equation step by step, we get

$x^{2}+9 x-1620=0$

Since $x>0$, the only solution is $x=36$.

The price of a package in the online store is $36 \mathrm{kn}$.

Note: If $x$ represents the price of paper in the bookstore, we get the equation: $\frac{180}{x-9}-$ $\frac{180}{x}=8$, or after rearranging $x^{2}-9 x-1620=0$. The solution to this equation is $x=45$, so $y=45-9=36$ is the price we are looking for.