A histogram is drawn with three columns whose widths are in the ratio 1: 2 : 4. The frequency densities of these classes are in the ratio 16 :12 : 3, respectively.

a. Given that the total frequency of the data is 390, find the frequency of each class. [3]

b. The classes with the two highest frequencies are to be merged and a new histogram drawn. Given that the height of the column representing the merged classes is to be 30cm, find the correct height for the remaining column.

c. Explain what problems you would encounter if asked to construct a histogram in which the classes with the two lowest frequencies are to be merged.