Hi

I would like to know details of Lux calculation and methods.

What would you like to know about it? Lux is simply a unit of measurement for the intensity of light. It is lumens/m^2

Light is somewhat of a complicated thing to quantify, so there are several ways of representing it mathematically. Lux is one of these ways.

I want to know lux,lumens etc

e.g.. I have 10 rooms 5 mtr length 6 mtr height, with gypsum board interoir
How many light fixtures required,give details about what height fixture should be from ffl

You need to chose the light fixture and lamps and obtain the IES file.

Need to know the reflectance of the surfaces.

Need to know the purpose of the room, to help decide what the IES recommend footcandles should be.

Mounting height of fixtures will be determined by the type of fixture, lamps, and CU (coefficient of utilization) rating of the fixture.

In other words, answering your question is not possible missing so much detail.