Answer :
r=x+9x
you add the invisible 1 beside the first x and 9x
so you would get
r=10x
you then which the sides of the equation
10x = r
you divide both sides by 10
x= 1/10r
you add the invisible 1 beside the first x and 9x
so you would get
r=10x
you then which the sides of the equation
10x = r
you divide both sides by 10
x= 1/10r