What is the constant of variation, k,

The K-constant variation is the factor of the increase-decrease relationship between the x-variable and y-variable which can be stated as y=k*x or x=y/k. For example, if y variable equal 5 and the x variable equal 2 then the k-constant variation equal 2 (calculation y=k*x --> 5=2*2.5). This constant shows the relationship between the variables.

The area of the wetland that will be covered in purple loosestrife 7 years from now is modeled by this expression.

500(1.2)^7

After evaluating the expression, the model predicts that approximately 1,792 acres of the wetland will be covered in purple loosestrife 7 years from now. This is not a valid prediction because the total area of the wetland is only 1,240 acres. So a constraint on the model is that the value of the expression 500(1.2)^t must be less than or equal to 1,240.