Answer:
The answer to your question is:
a) The gold cube is larger.
b) lenght = 1.67 cm
Step-by-step explanation:
Data
Platinum density 21.45 g/cm3 100 gram cube
Gold density 19.3 g/cm3 100 gram cube
Formula
 density = mass / volume
a) Calculate volume
 volume = mass / density
 
Platinum volume = 100 / 21.45 = 4.66 cm3
Gold volume = 100 / 19.3 = 5.18 cm3
b) Volume = lenght³
 4.66 cm³ = lenght³
 lenght = ∛4.66
 lenght = 1.67 cm