RBI Deputy Governor, K. C. Chakrabarty today said the apex bank will assess if the declining trend in inflation is sustainable, and accordingly take a decision on reducing interest rate. He said 5 per cent inflation is the comfort zone. The Reserve Bank is scheduled to review its monetary policy on September 17.After taking charge of the Finance Ministry this month, P. Chidambaram had said that high interest rates inhibit the investor, and are a burden on every class of borrower. He had also said that steps would be taken to bring down interest rates.