(C) Model and solve one-variable equations with variables on both sides of the equal sign that represent mathematical and real-world problems using rational number coefficients and constants
7.RP.2 Recognize and represent proportional relationships between quantities.7.RP.2.C
7.RP.2.C Represent proportional relationships by equations. For example, if total cost t is proportional to the number n of items purchased at a constant price p, the relationship between the total cost and the number of items can be expressed as t = pn.HSA.REI.2
HSA.REI.2 Solve simple rational and radical equations in one variable, and give examples showing how extraneous solutions may arise.