if we need to design lighting for any area with 800 lux, how many bulbs of say 60 watts we need to put per 100 sq.ft?

If the 60 watt lamp is an incandescent, really need to know the luminaire type, as an incandescent lamp is a point source.

Calculating without knowing the CU (Coefficient of Utilization) of the fixture will assume bare bulb lamp, and will need more lamps than necessary than with a fixture.

So, need to know lamp type and type of fixture.

Really need to know the finishes in the space also, so reflectance can be included in the calcs.

You mention Lux, are you in Europe, or otherwise not in North America?