Ms. Prudent will be retiring in 30 years from now. According to her estimates, after retirement she is going to need $12,000 per month for 15 years to maintain her lifestyle. She wants to start saving and investing from now to fulfill her post-retirement needs. How much does she have to invest per month for the next 30 years to afford her post-retirement cash flow requirements? Pre-retirement discount rate is 7% (annual) and post=retirement discount rate = 8.5% (annual).