Given a list of data, implement the following 4 methods using LINQ in a class that allows for managing cars:
1. MostExpensiveCar-returns the most expensive car in the car list.
2. CheapestCar - returns the cheapest car in the car list.
3. AveragePriceofCars - returns the average price of all cars in the car list. The average price is rounded to the nearest whole number.
4. MostExpensiveModelForEachBrandcalculates the most expensive car for each unique brand and returns the results as a Dictionary