Could not include namespace System.Threading.Tasks

Question

I am unable to include System.Threading.Tasks in my project.

I am Using Asp.net 2013 (4.5)

I am getting the following error -

The typ

Answer 1

System.Threading.Tasks.Task is in mscorlib which in .NET4.5. My project is not targeting, so in project properties need to change the target to 4.5.