Of my own devising it goes like this.I hope it is "realistic",easy and revealing (at least to me)

A "train" with a hole in the middle of its rear carriage speeds through the station at a speed of c/2.

Its length is 1 light second.

There is a stationary observer at the station

Inside the train a beam of light goes from the back of the train to the front and is reflected back to the rear (so it travels for 2 seconds in the train according to the reference frame of the train -and always in the direction of or against the direction of the motion of the train)

Then the beam passes through the hole at the rear and completes its journey to the observer at the station-it exits the train.

How much time has elapsed on the observer's watch (to include the time the light beam traveled in the carriage as well as the return journey. ?

I think I can see that the answer should be a little under 4 seconds and I also understand that t(prime) =t/sq.rt.(1-1/4) =1.155t but I am not sure as to how to put it all together.

Could the answer be 2 times the reciprocal of 1.155 plus 2 seconds? ie 3.732 seconds?

Or is the 2 nd half of the journey (outside the train) going to "simply" take another 1.732 seconds instead of 2 seconds -giving a total of about 3.46 seconds ?

Or maybe something different again?

Sorry I have no graphic skills to draw the schema but I hope it was clear enough (.