Question

How did you get -1? In the problem xm=x+z ,for x

Answer 1

Remember, we can do anything to an equation as long as you do it to both sides

and distributive proeprty, reversed
ab+ac=a(b+c)

xm=x+z
minus x from both sides
xm-x=z
xm-1x
undistribute x
x(m-1)=z
divide both sides by (m-1)
$x=\frac{z}{m-1}$