The X axis will not change since A is not going left or right of (2,2). You would count down 3 spaces for the y-axis and that would land you at -1 or you could solve by subtraction.
You need to form an algebraic equation. 4.5+h=7.3 therefore h= 7.3 - 4.5 when you take 4.5 to the other side it becomes negative therefore the answer is 2.8.