.NET Core 3.1 and Could not load file or assembly System.Data.Entity

The similar problem is written here, but not totally same.

I have a new Core 3.1 web project and old .netFramework 4.0 project working with EntityFramework (like BLL). I'm trying to create an instance of the class from that BLL and getting an error "System.IO.FileNotFoundException: 'Could not load file or assembly 'System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. No such file"

I've installed NuGet packages EntityFramework and EntityFrameworkCore, but it didn't help. In references of the Core 3.1 project I can't find any Entity library. How can I fix it?

Also I tried to add reference to a file System.Data.Entity.dll, but having another error then - "Reference assemblies should not be loaded for execution. They can only be loaded in the Reflection-only loader context. (0x80131058)"