Along distance runner does a first lap around a track in exactly 50 seconds. as she tires, each subsequent lap takes 20% longer than the previous one. how long does she take to run 3 laps?

Since only a few laps are involved, you can simply add up the times.
The second lap will take 50*1.2 = 60 seconds.
The third lap will take 60*1.2 = 72 seconds.

The total time for 3 laps will be (50 +60 +72) seconds = 182 seconds.