Write, read, and evaluate expressions in which letters stand for numbers (6.EE.2)

Write expressions that record operations with numbers and with letters standing for numbers; Identify parts of an expression using mathematical terms, view one or more parts of an expression as a single entity; 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).