Wade Ellis's and Denny Burzynski's "Solving Linear Equations and Inequalities: Linear Inequalities in One Variable"

Read the text until the section titled "The Algebra of Linear Inequalities." This part of the text is an introduction to linear equalities. As you can see from the given examples, inequalities are very similar to equations, except that they state that one expression is smaller (or greater) than another, rather than equal.