The faster gamma case drives both the longer-time and shorter-length ledgers. 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 faster triangle still gives exact time
Gamma 5/3 turns proper time 3 s into lab time 5 s.
3⋅35=5
The same gamma shortens length
The same gamma turns rest length 5 m into moving length 3 m.