4. Consider :13 = (f o g){2:, y). (a) What substitution 1: would you use to attempt to solve an ODE of this form? Compute d1: E. (b) For this substitution to work.J what functions must the partial derivatives of g depend on? (G) Choose 1\" and 9 so that this method will work and solve the ODE usng a substitution. (d) Name all theorems used in this exercise and label where they were used