To determine the price of the tablecloth, you should look at area of the original place mat and consider how much greater the area is of the tablecloth.
We know that each dimension will be 4 times longer which equals an area that is 4 x 4 = 16 times bigger.
Knowing the area is 16 times bigger, you should make the price 16 times higher.
I would certainly be willing to do that for you. But in order to write the composite function, I would first need to know the elemental functions ... f (x) and g(x).
