explanation for B:
from the question we know that:
SUM(EME) = 9.8m...where, SUM(EME) means sum of the experience of male employees, and m is no. of males.
SUM(EFE) = 9.1f

from B:
[SUM(EME)+SUM(EFE)]/m+f = 9.3
[9.8m+9.1f] = 9.3 (m+f)..solve this eqn for getting a ratio of m/f.

let Ym1 be the Year of experience of Male 1 and similarly Yf1 be the year of experience of Female 1

As per the problem statement = (Ym1 + ......YmN) / N = 9.8
= sum( Year of experience of all males ) = 9.8 N ..................(1)

Similarly sum ( Year of experience of all females ) = 9.1 M .........................(2)

Questions is to Find N / M ?

Statement 1 N = 52 ... but with this we can't find the ration of N / M .... hence insuffiecient

Statement 2 sum ( Year of experience of male + female ) = 9.3 ( N + M) ................... (3)

If we add equation 1 and 2 we get

sum ( years of experience of male + female ) = 9.1 M + 9.8 N = 9.3(N+ M) ( From equation 3)

hence 9.1 M + 9.8 N = 9.3 N + 9.3 M

From the above equation we can get the ration of N / M . hence statement 2 is sufficient .

Answer is B