in the ques a force is applied to the mass m on the top of the table such that it just slips.........this means that its limiting frictionnal force
let the applied force be F
so F= mew x m x g
now if we consider the table as the system , there will be a frictional force in the right direction.......and it will be equal to
mew x m x g due to newtons third law
now there is a frictional force in the left direction coz of friction between the floor and the table.........since the table is in equilibrium this must be balanced by the friction on top of the table