Approximately how much principal would need to be placed into an account earning 4.8% interest compounded monthly so that it has an accumulated value of $78,550 at the end of 38 years?

I'm assuming you mean to say that the clock already showed 10 seconds when she started the race.

It took her 5 seconds to run 100 meters since 15-10 = 5.

To find her speed, divide 100 over 5 to get 100/5 = 20 meters per second

20 meters per second is approximately equal to 44.7387258 miles per hour.

Something seems really off because the fastest record speed for a human runner was around 28 mph. Though of course, this is just a hypothetical math problem.