Rewrite as function as x; x = x + ((x - y) / z * 100)

We have
x = ((x - y)/z * 100)
To write it as a function of x, we'll have to take x on one side and the rest on other side of the equation.
x = x + ((x - y) / z * 100)
=> 0 = (x - y)/z * 100
=> 0 = (x - y)
=> x = y
You can now write is as y = x. y is a function of x now.