Two questions: are there any initial conditions? What have you done so far?
Ok, there's no initial condition.
Forum policy is not to simply solve problems for people. We are here to help you get unstuck if there's a part of the problem you don't understand. But you have to put forth the effort to solve the problem. If you think about it, this is better for you! You're not going to "own" the solution, and remember how to solve this kind of problem, if I just post a solution for you.