Answer:
y - x
Explanation:
You want the simplified form of |y -x| if y > x.
Absolute value
The absolute value function is defined as ...
|a| = a . . . . for a ≥ 0
|a| = -a . . . . for a < 0
Application
We have the expression |y -x|. Using the above function rule, it is ...
|y -x| = y -x . . . . for y -x ≥ 0 ⇒ y ≥ x
|y -x| = -(y -x) = x -y . . . . for y -x < 0 ⇒ y < x
The problem statement tells us we're interested in the case y > x, so the first version applies:
|y -x| = y -x . . . . if y > x