Changing only length changes the one-way travel time. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The shorter line gives the anchor delay
With length 12 meters and speed 3 meters per second, delay is 4 seconds.
12÷3=4
Doubling only length doubles the delay
With the same speed and length 24 meters, the delay becomes 8 seconds.