Answer;
-A model
Step-by-step explanation;
-A mathematical model is an abstract model that uses mathematical language to describe the behavior of a system. A Mathematical Model tries to copy how a real world thing works using equations.
-Usually a mathematical model describes a system by a set of variables and a set of equations that establish relationships between the variables. Variables may be of many types; real or integer numbers, for example.
-The Area A of a circle with radius r is given by the formula A = πr2. In this formula π ≈ 3.1416... is a number which is a constant, and A and r are variables or unknowns. A is called the subject of the formula.