Justin is planning on retirement investment, if invested at 6 percent per year (6%p.a. is APR, interest compounded monthly), he wish to have $3,500 of monthly income for 30 years. To date, he has saved $100,000, but he still has 20 years until he retires. How much money does he need to contribute per month to reach his goal? (Give your answer in 2 decimal places, provide your answer as a positive number.)