4 problems about ordinary and partial differential equation ode 1

Please help me with 4 questions about Ordinary and Partial Differential Equation (ODE).

Attached are related lecture notes. I will post these 4 questions when someone pick up this assignments. It is not too hard and not too much work. If you do 100% correct for this assignment, I will pay more tips. Hope an excellent tutor who is good at ODE can help me. Thanks a lot!