CCSS.Math.Content.6.EE.A.2 Write, read, and evaluate expressions in which letters stand for numbers.

• CCSS.Math.Content.6.EE.A.2a
  Write expressions that record operations with numbers and with letters standing for numbers.
• CCSS.Math.Content.6.EE.A.2b
  Identify parts of an expression using mathematical terms (sum, term, product, factor, quotient, coefficient); view one or more parts of an expression as a single entity.
• CCSS.Math.Content.6.EE.A.2c
  Evaluate expressions at specific values of their variables. Include expressions that arise from formulas used in real-world problems. Perform arithmetic operations, including those involving whole-number exponents, in the conventional order when there are no parentheses to specify a particular order (Order of Operations).