How can i get System.Reflection.IntrospectionExtensions for .NET 4.0?

I m new to .net,

Now when i run my source code,

It shows error like this.,

Could not load type 'System.Reflection.IntrospectionExtensions' from assembly 'System.Reflection, Version=4.0.0.0, Culture=neutral, PublicKeyToken=..'

I referrenced below link,

But it is not working,

Can anyone help me to fix this error?

Any help would be highly appreciated.

Thanks in advance.