4 (10 points). Consider the equation (x] + y' + y)dr - xdy = 0. (1) (a) Show that (1) is not exact, but becomes exact upon dividing by a + y'. (b) Solve (1) implicitly. That is, find U such that the level curves U(r, y) = c are solutions to (1). (c) Solve (1) explicitly. That is, isolate y by rearranging your answer in (b). (d) Check that your solution in (c) satisfies ry' = x- ty ty