Navkar Corporation Limited showed the inventory stock on S$$ptember $30,2017,$ is R$$75,000.$ From September $15$ to September $30,$ the gross sales of the company were R$$125,000$; Sales returns, R$$1200,$ goods purchased, R$$100000$; purchase returns were R$$650$; transportation$-$in R$$500.$ Find inventory cost as of September $15,$ if the company reported $18\%$ gross profit?