You want to sell e$-$book readers in Serbia and can't find a price point for it$,$ so you decide to use the iPhone index.

The price of an iPhone in Serbia $($including taxes, exchange rate, inflation$)$ is $$1020.$

The price of the same product in the U$.$S$.$ is $$820$

The price of your e$-$Book reader in the U$.$S$.$ is $$100,$ so for how much would you sell it in Serbia?