[tex]If\\\\\dfrac{H-W}{8}=m\qquad\text{multiply both sides by 8}\\\\H-W=8m\qquad\text{subtract H from both sides}\\\\-W=-H+8m\qquad\text{change the signs}\\\\\boxed{W=H-8m}[/tex]
[tex]If\\\\H-\dfrac{W}{8}=m\qquad\text{multiply both sides by 8}\\\\8H-W=8m\qquad\text{subtract 8H from both sides}\\\\-W=-8H+8m\qquad\text{change the signs}\\\\\boxed{W=8H-8m}[/tex]