Answer: 2.5 hours
30 min in, the jet bomber flew 250 miles, while the fighter jet has not left the base yet.
After 1 hour, the JB flew 500 miles, and the FJ flew 300. ( at this point the FJ has only been the air for 0.5 hours)
1.5 hours: JB = 750m FJ = 600m
2h JB = 1000m FJ = 900m
2.5h JB = 1250m FJ = 1200m
3h JB = 1500m FJ = 1500m
So the JB took 3 hours to fly to its target, while the FJ only took 2.5. Remember to subtract the initial 0.5 hours because the FJ left the base 0.5 hours after the bomber took off.