i hope im right this time

        public static string GetCarsWithTheirListOfParts(CarDealerContext context)
        {

            var cars = context.Cars
                .Include(c => c.PartCars)
                .ThenInclude(c => c.Part)
                .Select(c => new
                {
                    car = new
                    {
                        Make = c.Make,
                        Model = c.Model,
                        TravelledDistance = c.TravelledDistance
                    },

                    parts = c.PartCars
                        .Select(p => new
                        {
                            Name = p.Part.Name,
                            Price = $"{p.Part.Price:F2}"
                        })
                        .ToList()
                })
                .ToList();

            string json = JsonConvert.SerializeObject(cars, Formatting.Indented);
            return json;
        }