using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    static List<data> datas = new List<data>();

    public static void Main()

    {

        Console.WriteLine("Hello World");

        datas.Add(new data { Emissivity = 100, Temperature = 200 });

        datas.Add(new data { Emissivity = 200, Temperature = 300 });

        datas.Add(new data { Emissivity = 300, Temperature = 400 });

        datas.Add(new data { Emissivity = 400, Temperature = 500 });

        Console.WriteLine("{0}", getTemperature(250));

        Console.WriteLine("{0}", getTemperature(300));

        Console.WriteLine("{0}", getTemperature(350));

    }

​

    static double? getTemperature(double emissivity) {

        return datas.OrderBy(e => e.Emissivity).FirstOrDefault(e => e.Emissivity >= emissivity)?.Temperature;

    }

    public class data {

        public double Emissivity { get; set; }

        public double Temperature { get; set; }

    }

}