A How To on Linear Systems with an equation example and step-by-step instructions.
Music is "Painted Sun In Abstract" by Trent Reznor & Atticus Ross (Soundtrack to "The Social Network").
No copyright infringement intended. I do not own this soundtrack or the rights to it.
Source: Mr. Hennen
Eight problems for you to solve yourself.
Source: McDougal Littel (Algebra 1)