How do you rewrite the equation -8x-5y-45?

-8x-5y-45 is not an equation. An equation requires an equal sign in there somewhere. If you meant -8x-5y=45, then there are many ways to rewrite it, such as -(8x+5y)=45, or 8x+5y=-45, or 8x=-(45+5y), to name three. If you meant -8x-5y=-45, then you're probably looking for 8x+5y=45.