Please tell me how to solve this optimization problem.

You and your friends are at a lake. You plan to race to a platform which is floating 500 feet out in the water and 1000 feet down the shore from where you are standing. You can run on land at 8 miles per hour and you can swim at 2 miles per hour. How far should you run along the shore before you jump into the water in order to minimize the amount of time it takes you to reach the platform? Give your answer in feet