The fourth vertex has a y-coordinate of 2, so it must be somewhere along the
line y = 2:
That will make the top and bottom sides of the trapezoid the parallel bases.
The formula for the area of a trapezoid is
Here it’s given that the area is 7.5, and you can see from the figure that one
base is 6 and the height is 2. That’s enough to solve for the other base.
The top base is 1.5, and for the four vertices to be consecutive, the
coordinates of the fourth vertex are (1.5, 2).