Answer:
Quite simply. The answer is X=6
Since you have a full fraction, you can find a common denominator in both fractions and multiply. (The common denominator would be 8, so you would multiply 4 by 2 to get 8. Do the same thing to the top, do multiply 3 by 2 to get 6). Now the fraction is 6/8, and since it's equal to incomplete fraction, you know X is 6.
Jenny won the race as she finished the race much more quickly and has greater average speed than Lester.

Jenny: distance/time = 100/15.2 = 6.58 m/s = 6.6 m/s
Lester: distance/time = 100/15.7 = 6.37 m/s = 6.4 m/s