In A frame, a light source at rest located at x = 0 emits a pulse P_1 at t_1 = 0, emits another pulse P_2 at t_2 = t. A’ frame moves with constant speed V along X axis with A frame. Observer in A’ at X’ = 0 receives P_1 at t_1’ = 0, X_1’ = 0 (i.e. P_1 was emitted when the origin of A and A’ were exactly at the same location). Find t’ when observer at X’ = 0 receives P2 in the A’ frame.

I know that it has to do with special relativity and time dilation but I don't know where to start and am confused on how to solve it.