In an investment problem, amount invested is in units of $1000, and total $6000 is available for investment. There are three possible investments with return amounts indicated. Investment $1000s 0 1 2 3 4 5 6 Return 1 10 25 35 55 75 100 Return 2 5 15 25 35 60 80 Return 3 10 25 45 65 0 0 0 3 15 Find the optimum investment distribution.