Don't know how to use namespace of one project in another

Question

I'm new to C# and JetBrains Rider and I'm having trouble using a namespace of a project in another project. I have one project with a namespace called math which I want to test through unit tests in a different project. The problem is that the namespace cannot be found.

Solution Setup

Any help?

I updated both Target Frameworks to .NETFramework v4.7.1.

I tried using references by right click on test project Properties -> Reference Paths and then adding the path of project directory and path of script directory but to no avail.

• Update

@gunr2171 The problem is that I cant add a reference or atleast I dont know how. The reference option isn't availible for the project. Options