Answer:
1260
Explanation:
Given : Jackie ran fifty yard at an average speed of 21 feet per second.
To Find: what was her average speed in feet per minute?
Solution:
Speed of Jackie = 21 feet per second.
60 second = 1 minute
1 second =

Now we are supposed to convert the speed in feet per minute
Now , 21 feet per second =
feet per minute
=
feet per minute
Hence her average speed in feet per minute is 1260 feet per minute
Thus Option A is correct.