Amit, Akash and Akshay start a business together. Investment made by Amit is Rs. 2,000 more than that of Akash and Rs. 4,000 more than Akshay. Amit and Akash invest for 6 months each and Akshay invests for 8 months. If ratio of profit at the end of the year is 9 ∶ 6 ∶ 4, then what was the total investment made by them in one month?