Error trying to install NuGet package in VS 2017

[Bluenose]

Hello

I am trying to install Install-Package WebHelpers and Install-Package System.Web.Help ers.Crypto via NuGet in Visual Studio 2017 but get the following errors respectively:

Install-Package : Project 'Default' is not found.
At line:1 char:1
+ Install-Package WebHelpers -Version 4.0.2
+ ~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~ ~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Default:String ) [Install-Package], ItemNotFoundExc eption
+ FullyQualifiedE rrorId : NuGetProjectNot Found,NuGet.Pac kageManagement. PowerShellCmdle ts.InstallPacka geCommand

and

Install-Package : Project 'Default' is not found.
At line:1 char:1
+ Install-Package System.Web.Help ers.Crypto -Version 3.2.3
+ ~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~ ~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Default:String ) [Install-Package], ItemNotFoundExc eption
+ FullyQualifiedE rrorId : NuGetProjectNot Found,NuGet.Pac kageManagement. PowerShellCmdle ts.InstallPacka geCommand

What am I doing wrong, please?

Thank you.