Answer: r=L - s / L
s=l(1−r)
Step 1: Flip the equation.
−lr+l=s
Step 2: Add -l to both sides.
−lr+l+−l=s+−l
−lr=−l+s
Step 3: Divide both sides by -l.
−lr
−l
=
−l+s
r=
l−s
l
