You cannot run that code just by pressing the green run button in the editor, and you cannot run that code just by invoking the function name. If you were to try to do either one of those, then MATLAB would not know what values to use for the input arguments Width and Area.
When you run a function, MATLAB never looks in your current workspace for variables with the same name as the input parameters. For example,
then MATLAB will never see that function has an input named Width and so look in the calling environment to see if a Width exists there to use.
When you want a function to use a parameter, you need to pass in the parameter when you invoke the function. For example, either of
Width = 7
Area = 19
Y = YoungJay(Width, Area)