If both J & B work they will finish the job in J*B/(J+B) hrs.
Also given both J&B are even.
Lets start with statement B
(J+B)^2 = 400
If J & B were equal then J=B=10
They will finish the work in 5 hrs i.e 5 PM, statement A is different hence we know J & B are not equal. Sufficient but before we jump to C lets look at statement A alone
J & B finish the job by 4:48p.m they take 4 48/60 hrs = 4 4/5 = 24/5
So we know J*B/(J+B) = 24/5
since J and B are even they can't be fractions, hence
J*B has to be a multiple of 24
J+B has to be a multiple of 5
since J & B are even J+B can only be multiples of 10.
Lets assume J=B and start plugging in values
when J*B/(J+B) = 48/10
J+B = 10, J=B=5 so J*B = 25 too small
when J*B/(J+B) = 96/20
J+B = 10, J=B=10 so J*B = 100 too big
when J*B/(J+B) = 144/30
J+B = 30, J=B=15 so J*B = 225 too big
J*B values keep increasing and will never equal the value derived by assuming j&B are equal.
Hence answer should be A.