A body moving along a straight line traversed one third of the total distance with a velocity `4 m//sec` in the first stretch. In the second strech the remaining distance is covered with a velocity `2 m//sec` for some time `t_(0)` and with `4 m//s` for the remaining time. if the average velocity is `3 m//sec` find the time for which body moves with velocity `4 m//sec` in second strecth: