The answer in fraction form is (9/2, 9/2), which in decimal form it would be (4.5, 4.5)
To get this answer, you add up the x coordinates of each point and divide by 2. So we'll have (4+5)/2 = 9/2 = 4.5
The same will apply to the y coordinates as well: (5+4)/2 = 9/2 = 4.5