Maximum number of elements in B could be 62.
(1,2,3,4, ....................61,62,)
for every element x greater than 62 we have (125-x)
For example 63 +62 = 125
64 + 61 = 125
......................100+25 =125
Therefore (1,2,3,4, ....................61,62) would be the maximum subset.