A trough has a semicircular cross section with a radius of 3 feet. Water starts flowing into the trough in such a way that the depth of the water is increasing at a rate of 2 inches per hour.

a. Give a function w = f(t) relating the width w, in feet of the surface of the water to the time t, in hours.

b. After how many hours will the surface of the water have width of 4 feet? (Round your answer to two decimal places.)

I am really confused on how to approach these two questions...Any help is appreciated!