Answer:
Zero
Step-by-step explanation:
The work done on an object is given by:

where
F is the force applied on the object
d is the displacement of the object
is the angle between the direction of the force and the displacement
In this problem, you are pushing again a stationary wall: this means that the walls does not move. As a result, the displacement is zero: d=0. Therefore, the work done is also zero: W=0.