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.