There is no difference here as you can say
In either case, the graph is "stretched" by 7. In the first case, 7f(x)+ 2, the distance between high and low values of the graph is stretched by 7 while the distance from the x-axis to some fixed point on the graph stays the same. In the second case, 7f(x)+ 14, the distance between high and low values of the graph is stretched by 7 and the distance from the x-axis to some fixed point on the graph is also stretched by 7. So it is all a matter of "what do you [i]mean[/b] by "stretched"?