This can be solved without Alger=bra ... just some serious Thinking.
have a 1500-meter race.
beats by 30 meters and by 100 meters.
By how much would beat over the full distance
. . if they both ran as before?
When ran 1500 meters:
. . ran only 1470 meters,
. . and ran a mere 1400 meters.
Hence, speed is only of speed.
When runs 1500 meters,
. . runs only: . meters.
Therefore, beats by about: meters.