Two and a half laps
Julia swims (21 x 7) = 147 laps.The way the question is worded, Carol's existence is irrelevant.
A grand total of 8 laps or 16 lengths. Each person swims two lengths which is 50 yards. There are also 50 yards of each stroke in the following order: butterfly, backstroke, breastroke, and freestyle. Each person swims 1 stroke for their entire 50.
24 divided by 8 is 3, which means she can run 3 laps per minute. Assuming she doesn't slow down she can run 3*12, or 36 laps in 12 minutes.
There are four people on a relay, so in a 200 free relay each person swims a 50 free.
In motocross racing there is not a set amount of laps it is asmany laps you can do in the set time (A race is normally between 20-40 minutes depending on how old you are etc)
How many laps in a Triathlon, depends on the distance of the race. Most "sprint" triathlons have a swim that is 500 yards or 750 yards. In a 25 yard pool, that is 20 to 30 laps. Most other triathlons are open water swims, ranging from 1.5Km for Olympic distance events up to 3.8Km for what is commonly referred to as Ironman distance.
About 100 to 150 caloires per 30 minutes, of swimming laps.
Most high school tracks are 1/4 mile. 20 laps would be 5 miles.