Mathematics · Simple Interest

Aman needed ₹30,000 for a start-up and split the sum between two private lenders under simple-interest terms: Lender A charges 9% p.a. (simple interest) Lender B charges 6% p.a. (simple interest) Aman kept both loans exactly 4 years and then made a single lump-sum payment that settled only the accumulated interest, which came to ₹9,600. After preparing his books of account, Aman discovered that if he had interchanged the principal amounts taken from the two lenders, his four-year interest outgo would have been ₹1,200 less than what he actually paid. How much of the original ₹30,000 did Aman borrow at 9% p.a. from Lender A?