The ratio of the surface areas of similar solids is equal to the square of their scale factor and that the ratio of their volumes is equal to the cube of their scale factor.
You can set up an system of equations
x=2y+8
x-y=25
Substitute x in to the second equation
2y+8-y=25
y+8=25
y=17
Substitute the y back in to the first equation.
x=2(17)+8=42
