Step-by-step explanation:
Work done by gravity is given by the formula,
 W = 
 ......... (1)
It is known that when levels are same then height of the liquid is as follows.
 h = 
 ......... (2)
Putting value of equation (2) in equation (1) the overall formula will be as follows.
 W = 

 = 

 = 0.689 J
Thus, we can conclude that the work done by the gravitational force in equalizing the levels when the two vessels are connected is 0.689 J.