Answer:
4 g / cm^2
Step-by-step explanation:
The density is defined is
where m is the mass of the object and V is its volume.
Now in our case, we see that the cube weighs M = 240 g and has a volume of
![V=3\operatorname{cm}*5\operatorname{cm}*4\operatorname{cm}=60\operatorname{cm}^3]()
With the value of M and V in hand, we now calculate the density
![p=\frac{240g}{60\operatorname{cm}^3}]()
![p=\frac{40g}{\operatorname{cm}^3}]()
which is our answer!