So given that the object has no acceleration
So net force on the object must be zero (from Newton's second law, F=ma)
Force of friction on the object is,
where mu is the coefficient of friction and N is the normal force,
Here the normal force is just the weight of the object,
so,
And so this has to be balanced by the applied force in the opposite direction to friction force,
Result: Applied force is 3N.