A red light flashes at position xr = 3.00 m and time tr = 1.00*10^-9s, and a blue light flashes at xb = 5.00 m and tb = 9.00*10^-9s, all measured in the S reference frame. Reference frame S' has its origin at the same point as S at t = t' = 0; frame S' moves uniformly to the right. Both flashes are observed to occur at the same place in S'. (a) Find the relative speed between S and S'. (b) Find the location of the two flashes in frame S'. (c) At what time does the red flash occur in the S' frame? I don't understand how to start part a. Any help would be great! thx!