Explanation:
The given data is as follows.
          Width of Styrofoam = 24.0 cm
           Length of Styrofoam = 36.0 cm
           Height of Styrofoam = 5.0 cm
Therefore, volume of the Styrofoam will be calculated as follows.
                   Volume = length × width × height
                                 =  (36.0 × 24.0 × 5.0) 
                                  = 4320 
or,                             = 
As Styrofoam partially sinks at 3.0 cm and total height of Styrofoam is 5.0 cm. Hence, height of Styrofoam above the water is (5.0 - 3 cm) = 2 cm.
So, volume of water displaced is as follows.
           24.0 cm × 36.0 cm × 2.0 cm
          = 
Hence, mass of displaced water is as follows.
                  mass = density × volume
                            = 
                            = 
Since, book is placed on the Styrofoam. Therefore, mass of water displaced is also equal to the following.
              Mass of water displaced = mass of book + mass of Styrofoam
                    = 1500 g + mass of Styrofoam
 = 1500 g + mass of Styrofoam
                    (1730 - 1500) g = mass of Styrofoam
                    mass of Styrofoam = 230 g
Therefore, calculate the density of Styrofoam as follows.
                    Density =  
   
                                  =  
 
                                  = 
Thus, we can conclude that the density of Styrofoam is  .
.