Answer:
(5.5, -3.5)
Step-by-step explanation:
As you can see in the figure, the fourth vertex is (5.5, -3.5)
If you observe carefully the vertex given, you will see that there are two vertex with same coordinates in x axis:
And one vertex has other coordinate in x axis, it is: (5.5, 4.4)
To form a rectangle, you need a fourth vertex that will have same coordinate in x than (5.5, 4.4) and same coordinate in y axis as (-1.2, -3.5),
Then the fourth vertex coordinate is (5.5, -3.5)