Salaries
========

Save all functions into the same file named :file:`salaries.py`.

#. Write the function :py:func:`apply_percentage` that given a 
   quantity and a percentage, returns the result of applying that
   percentage to the given quantity.  

#. Write the function :py:func:`lustrum` that given two different years (the
   first year lower than the second one) returns the number of full 5 year
   periods (lustrum) that there are between them. For example: between 2003 and
   2016 there are two lustrums.
   
#. To calculate the salary of its workers, a company starts from a
   fixed base salary, and a variable salary made of two parts: the
   first one is calculated applying a percentage to the quantity of
   sales made by that worker and the second part is calculated from a
   bonus that is applied by each full lustrum since the worker started
   to work for the company.

   Write the function :py:func:`salary` that takes the fixed base
   salary, the sales, the applied percentage, the seniority bonus,
   (all ``float``), the year in which the worker was hired by the
   company and the present year (``int``, indicating the century),
   returns the final salary applying the explained method. This
   function must call both previous functions.

These functions must pass the following doctest:

   .. literalinclude:: salaries.txt
      :language: python3
      :lines: 2-

   .. note::

      You can download the file with tests :download:`salaries.txt <salaries.txt>`

.. rubric:: Solution

A solution of these functions is provided in file :download:`salaries.py
<solutions/salaries.py>`.