A. 6 Months
B. 7 Months
C. 8 Months
D. 9 Months
=> A's investment = Rs.85000/-
=> Investment Duration = 1 Year = 12 Months (because profit is being calculated at the end of the year)
=> B's Investment = Rs.42500/-
=> Say, duration of investment by B is N
=> Ratio of investment of A and B = 85000 x 12 : 42500 x N
=> 1020000 : 42500N
=> Ratio of Profit = 3 : 1
=> 1020000 : 42500N = 3 : 1
=> N = 8
So, B's investment must be for 8 Months