(1) When the elder brother is behind the younger brother, 2vt-3=vt- 1, vt=2, 2vt=4.
(2) When the elder brother is in front of the younger brother, 2vt-vt=3+ 1, vt=4, 2vt=8.
When my brother runs 4 meters or 8 meters, the distance between them is 1 meter.