Entity-Framework is in costant development, and you may be using it in many projects.
So, you may be using different versions.

There are many ways to check which version is currently in use

Get-Package

Open the

Package Manager Console

And use the command: Get-Package

Reference Section

Expand the Reference section and select Properties

There you can find the Entity-Framework you are using.

packages.config

Open the packages.config file in the project root.
Search for the Entity-Framework row in this file.