Since the -13 has the absolute value signs next to it, the 13 becomes a positive, but there is a negative outside the absolute value, and the negative sign and the absolute value sign cancelled previously, so the expressions is now -13 The absolute value signs cancel out a negative only inside the signs, not outside, so the negative sign in the outside keeps.
100%/x%=80/20
(100/x)*x=(80/20)*x - we multiply both sides of the equation by x
100=4*x - we divide both sides of the equation by (4) to get x
100/4=x
25=x
x=25
