As seen by one observer, two recrackers are set o at the same place but separated by 4 seconds in time.

As seen by one observer, two recrackers are set o at the same placebut separated by 4 seconds in time.As observed by a second observer, moving with respect to the rst,the two recrackers detonate at places separated by 3 light-seconds inspace.As observed by this second observer, how much time is there between the two detonations?How fast is this second observer moving with respect to the rst?