Kinematics 3

A train starts from station A with uniform acceleration $a_1$ for some distance and then goes with uniform retardation $a_2$ for some more distance to come to rest at station B. The distance between station A and station B is 4 km and the train takes $\dfrac1{15}$ hours to complete the journey. If the accelerations are in $\text{km/min}^2$ then find the value of $\dfrac1{a_1} + \dfrac1{a_2}$ is: $\text{\_\_\_\_\_\_\_\_\_\_}$ .