Answer with Explanation:

Let investment in 12% stock be Rs. x.

Then, investment in 15% stock = Rs. (12000 - x).

Therefore,12/120 x x + 15/125 x (12000 - x) = 1360. 

=> x/10 + 3/25 (12000 - x) = 1360. 

=> 5x + 72000 - 6x = 1360 x 50

=> x = 4000.