I assume the volume of the larger pyramid is 108 ft^3, not 108 ft^2.
The scale factor of edges of two solids is x.
The scale factor of their areas is x^2.
The scale factor of their volumes is x^3
The areas have a scale factor of 18/8 = 2.25
The length have a scale factor of sqrt(2.25) = 1.5
The volumes have a scale factor of 3.375
108/3.375 = 32
Answer: 32 ft^3
