What is the source of the input energy for the cogeneration of energy?

Well it depends.
 For example a saltwater distillation process requires heat that turns the saltwater into steam - the steam runs through a condensor to produce drinkable water. However, that same steam could also be used to drive a steam turbine to generate electricity, before being condensed back into water. 

The source of the original heat may have been coal, oil, gas, or other fuel. But now you've gained maximum benefit from the same heat unit.
XD :)

Awoodchuck would chuck all the wood he could chuck if a woodchuck could chuck wood.

Multiply the 3 dimensions, assuming it is a rectangular cuboid, to get the volume in cm³ divide mass by volume to get density in g/cm³