6.AT.C.8: Solve problems in context by writing and solving equations and interpreting the solutions in context. a. Explain that a variable can represent an unknown number and use substitution to determine whether a given number makes an equation true. b. Write and solve one-step equations of the form x + p = q, x − p = q, px = q and x/p = q for cases in which p, q and x are all nonnegative rational numbers. c. Represent solutions of such equations on a number line.