the freezing point of a 4%(w/w)aqueous solution of 'A' is equal to the freezing point of 10%(w/w)aqueous solution of'B'.If the molecular weight of'A'is 60, then molecular weight of 'B' will be:[Aand B are non-volatile non-electrolytes]

Since both the solutions are aqueous solutions, the actual freezing point of solution( if no solute was added) would have been 0^OC.
given that both the solutions have same freezing point, one can say that the depression in the freezing point would also be the same for both the solutions, thus, one can write,

Thus,
Putting the above values, one can easily get the answer