There are times where we are interested in expressing data sets into mathematic models. One of the most commonly used is the linear model, where the dependent variable has a linear relation with the independent variable. A special case of a linear model is the direct relation or proportion, where the variables relate in the form:
Where k is an arbitrary constant.
We know y=22.5 when x=0.9. This can be used in the equation above to find the value of k: