Spring, Charge and Block

A small block having charge $Q$ placed on a frictionless horizontal table is attached to one end of a spring of force constant $k$ . The other end of the spring is attached to a fixed support and the spring stays horizontally in relaxed state. Another small block carrying a negative charge $-q$ is brought very slowly from a great distance towards the former block along the line coinciding the axis of the spring.
Find extension in the spring when both the blocks collide.

Details.and Assumptions
1) $q=1$
2) $Q=2$
3) $\epsilon_{0}=3$
4) $k=4$