This problem illustrates the typical approach for creating a model. Use lower case letters.(a) We want to express the area of a circle, A, as a function of its circumference, c.Start with the basic formula we know for the area of a circle in terms of its radius.A=Because we want this area formula in terms of circumference and not radius, we need another formula that will allow us to replace in terms of c. The formula that has both r and c in it is the circumference formula for a circle.c=Solve this equation for r.r=Use this to replace r in terms of c in our area formula. Note the function notation also reminds us that the independent variable should be c when we are done.A(C)=Now try this approach on the following problem. Don't forget, if you need, there is a reference sheet of geometry formulas in the description of this assignment.(b) Express the diagonal of a rectangle, D, in terms of its width, w, if the area of the rectangle is 13 square feet.D(w) =