Precalc question (googling this question can give you diagram)

Question

A trough has a semicircular cross section with a radius of 5 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.

Give a function w = f(t) relating the width w of the surface of the water to the time t, in hours. Make sure to specify the domain and compute the range too.

(Answer of f(t) is 2√(25-(t/6-5)^2), but please explain to me how this is the answer)

Answer 1