Explanation

Jhumri Telaiya is a town in Koderma district of Jharkhand, in the Damodar valley — famous since the 1950s for its Radio Ceylon/Vividh Bharati listenership. The Mandar hills tract referred to in the question lies in Jharkhand (the Hazaribagh–Dhanbad region, noted in state geography for sandy soil). Neither Assam nor West Bengal fits either place. Hence Jharkhand.