A LIVING ROOM HAS DIMENSIONS 3.5M X4.2M X4.2M .WHAT IS THE PRESSURE EXERTED BY THE AIR ON THE FLOOR IN THE ROOM

Answer 1

14.7 lb/in^2 * (4.2*4.2) m^2 * (39.37in/m)^2 = 401,926 lb
assuming a square room...
assuming the air pressure inside is the same as outside ...

Answer 2

You have to assume air pressure is on both sides of the floor, generally, so the net force is zero. Thus, the net pressure is zero.