SOLUTION: 2 spheres of the same density have a ratio of 9 to 16 in surface area. If the small sphere weighs 15 kg, what does the other sphere weighs.

If the values of the surface area are in proportion 9:16, it means that

their radii are in proportion 3:4.


Then their volumes are in proportion  = 27:64.


Hence the weight (or better to say, the mass) of the larger sphere is

     =   kilograms = 35.555 kilograms.    ANSWER


(Assuming that they are continuum media with no voids inside, and are made of the same material).

    Kilograms as the measure of weight are not in use since 60-ies of the past century.


    Since that time and till now, only Newtons are used as a measure of forces (and as a measure of weight, in particular) 
    everywhere (excluding US), and everywhere in Physics, including US).


    Kilograms are still used as a measure of mass).