CCSS.Math.Content.6.EE.B.5 - Understand solving an equation or inequality as a process of answering a question: which values from a specified set, if any, make the equation or inequality true? Use substitution to determine whether a given number in a specified set makes an equation or inequality true.
CCSS.Math.Content.6.EE.B.6 - Use variables to represent numbers and write expressions when solving a real-world or mathematical problem; understand that a variable can represent an unknown number, or, depending on the purpose at hand, any number in a specified set.
CCSS.Math.Content.6.EE.B.7 - Solve real-world and mathematical problems by writing and solving equations of the form ?? + ?? = ?? and ???? = ?? for cases in which ??, ?? and ?? are all nonnegative rational numbers.
CCSS.Math.Content.6.EE.B.8 - Write an inequality of the form ?? > ?? or ?? < ?? to represent a constraint or condition in a real-world or mathematical problem. Recognize that inequalities of the form ?? > ?? or ?? < ?? have infinitely many solutions; represent solutions of such inequalities on number line diagrams.