Hexamethylenediamine (MM 5 116.2 g/mol), a com-
pound made up of carbon, hydrogen, and nitrogen atoms are used in the production of nylon. When 6.315 g of hexamethylenediamine is burned in oxygen, 14.36 g of carbon dioxide and 7.832 g of water are obtained. What are the simplest molecular formulas for this compound?

Planning for solving this question -
First get the empirical formula from given information and then take ratio of molar mass with empirical formula mass to get n value .
                          Molecular formula = (Empirical formula)_n
Now the aim is to get the empirical formula.
Now you remember that  empirical formula is the lowest or simplest whole number ratio of the elements in the compound.
I need to know mass of each element to know moles of each element and then we can work out the ratio to know empirical formula.
Question is how to know mass of each element?
Read the question carefully and split the information in different parts.
Now element's in our compound are carbon ,hydrogen and  nitrogen.
It is the combustion of the compound
It means reaction is -
(C,H,N)  + O₂ ----.  CO₂ + H₂O  + oxide of nitrogen.
Total mass of sample hexamethylenediamine = mass of carbon + mass of nitrogen + mass of Hydrogen.  -----(  1 )   

Carbon of the sample is completely converted in to 14.36 g CO₂ gas .
Use this information to know moles and then mass of Carbon.
grams CO₂ ---> moles of CO₂ ----> moles Carbon ---> grams of carbon.
Similarly use mass of water to know moles of H and then grams of H
Grams of water ---> moles of water ----> moles of H ---> grams of hydrogen.
Now you have grams of Hydrogen and carbon
use information -1 mentioned earlier to know that mass of N
Convert mass of N to moles of N
Now you have moles N ,C and H.
Take the simplest ratio of these moles and that will give you empirical formula.
Get n(factor) = molar mass / empirical formula mass
  Molecular formula = (Empirical formula)_n