Mujeeb wrote:
Even I have obtained the result by using the function PMT. But I still
consfuse that how PMT function works, what is its background / machanizm.
When we give parameters in this function, how this function manipulate the
parameters and give us result?

Take a look at the mathematical formula at the bottom of the Help page
for the PV() function. Algebraically solve for "pmt". If that does
not sufficiently answer your question, you might google for "present
value formulas" (without quotes). For example,
http://en.wikipedia.org/wiki/Present_value might be useful.