ASP.NET Web API 2 .NET Core project gives build error with .NET 4.6.1 Unit Testing Project

I am working on ASP.NET Web API 2, added a Unit Test Project for Unit Testing but it is giving me a build error like this in one of method

uses 'System.Runtime, Version=4.2.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' which has a higher version than referenced assembly 'System.Runtime' with identity 'System.Runtime, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

I have done all possible solutions,i think its an issue of .NET core with .NET statndard library

Please Help !