The mass of solid 'a' is 4000 grams
How to find the ratio of the masses?
We are given the parameters as:
the surface area of b is 40.32cm²
the surface area of a is 28cm²
the mass of b is 6912 grams
The ratio of masses will be the 3/2 power of the ratio of areas for the same density and shape of material.
Mass ratio = A/6912 = (28/40.32)^(3/2)
A = 6912/1.728 = 4000
The mass of 'a' is 4000.